Do fixed geographic features such as coastlines and rivers determine town locations, or can historical events trap towns in unfavourable locations for centuries? We examine the effects on town locations of the collapse of the Western Roman Empire, which temporarily ended urbanisation in Britain, but not in France. As urbanisation recovered, medieval towns were more often found in Roman‐era town locations in France than in Britain. The resetting of Britain's urban network gave it better access to natural navigable waterways, which mattered for town growth from 1200 to 1800. We conclude that history trapped many French towns in suboptimal locations.

Our world is increasingly urbanised, with large cities located in many different environments. While some cities appear well situated, others are hampered by poor access to world markets or threatened by environmental hazards. But it is difficult to tell whether cities are in fact mislocated, because locational advantages that we cannot quantify could offset the costs that we do observe. To investigate whether cities are mislocated, one might examine whether cities that are devastated then relocate, and if so – where. But in recent years a growing literature, going back to Davis and Weinstein (2002), finds that cities are remarkably resilient and recover from shocks. This has generally been interpreted as evidence that locational fundamentals play an important role in pinning down the location of cities. At the same time, Bleakley and Lin (2012) show that once cities develop in particular locations, they persist even when the factors that led to their emergence are no longer important. We contribute to this literature by examining the impact on urban locations of a shock that was sufficiently large to eliminate an urban network. Specifically, we study the collapse of the Western Roman Empire around the middle of the first millennium CE, which wiped out the towns in what is now Britain, but not in France.1 We are, to the best of our knowledge, the first to examine whether in the aftermath of such a devastating shock, an urban network that gets a fresh start reconfigures in new locations. We also examine whether such a reconfiguration improves towns’ locations in terms of their first nature locational fundamentals. In order to carry out our analysis, we develop a new dataset, which tracks the locations of towns in parts of north‐western Europe over two millennia. We begin our empirical investigation by considering what may happen if an urban network is wiped out and restarts, while an initially similar urban network remains intact. In this event, the evolution of town locations may follow one of three scenarios. First, if first nature locational fundamentals, such as coastlines, mountains and rivers, consistently favour a fixed set of locations, then these locations would be home to both surviving and re‐emerging towns, resulting in high persistence of locations in both urban networks. Second, if first nature locational fundamentals or their value change over time and these fundamentals affect productivity more than the concentration of human activity (including the value of past investments), then both urban networks would similarly shift towards locations with improved fundamentals. Finally, if first nature locational fundamentals or their value change but these fundamentals are less important for productivity than the concentration of human activity (including the value of past investments), then the locations of urban networks are path dependent. In this case, the urban network which was wiped out would re‐emerge in locations with better first nature locational fundamentals, while its counterpart would remain in its original locations due to path dependence. Even this third scenario has two variants: one in which the differences in the value of first nature locational fundamentals between locations are small and inconsequential (for example locations in a wide prairie or along a slow flowing river) and another in which they are consequential, leaving some towns in unfavourable locations. To investigate the empirical relevance of these different scenarios, we trace the locations of towns in north‐western Europe back to the Roman era. Around the dawn of the first millennium, Rome conquered and subsequently urbanised areas including those that make up present day France and Britain (as far north as Hadrian's Wall). In the subsequent centuries, the Roman towns in France and Britain developed similarly in terms of their institutions, organisation and size. Around the middle of the fourth century, however, their fates diverged. Roman Britain suffered invasions, usurpations, and reprisals against its elite. Around 410 CE, when Rome itself was first sacked, Roman Britain's last remaining legions, which had maintained order and security, departed permanently. Consequently Roman Britain's political, social and economic order collapsed and its towns no longer functioned from 450–600 CE.2 A recent quantitative analysis (Faulkner, 2000) shows that the number of occupied rooms in private buildings in 16 major Roman‐British towns fell by about 90% from the early fourth century to the early fifth century and, by the middle of the fifth century, even the remaining homes were abandoned. The Roman towns in France also suffered when the Western Roman Empire fell but many of them survived and were taken over by Franks. So while the urban network in Britain effectively ended with the fall of the Western Roman Empire, there was much more urban continuity in France. The divergent paths of these two urban networks allow us to study the spatial consequences of the resetting of an urban network, as towns across north‐western Europe re‐emerged and grew during the Middle Ages. In comparing Britain and France during the High Middle Ages we note that both were again ruled by a common elite (Norman rather than Roman), and had access to similar production technologies, inasmuch as these may have affected the location of towns. Our empirical analysis of town locations uses a grid of 1 kilometre2, spanning the land area of the Roman Empire at its greatest extent, around the time of Emperor Trajan's death in 117 CE. Focusing on north‐western Europe, we map onto this grid locational fundamentals and the locations of towns from the Roman and medieval eras to the present day. We define persistence relative to Roman‐era towns as an odds ratio: the probability of finding a later town near the site of a Roman town, divided by the probability of finding a later town near the site without a Roman town. We find that from the Early Middle Ages (700–900) until the dawn of the Industrial Revolution (circa 1700), the persistence of towns compared to the Roman era in France was approximately three times higher than in Britain. The differences in persistence are still visible today; for example, only two of the 20 largest cities in Britain are located near the site of Roman towns, compared to 16 in France. Our finding that the urban network in Britain relocated more than in France between the Roman and medieval eras is consistent with the third scenario outlined above, where town locations are path dependent. This finding is robust to many specification checks, including widening or narrowing the measure of geographic proximity; restricting the continental area to the north of France, which is more similar to Britain, or widening it to encompass all the area of north‐western Europe that lay within the boundaries of the Roman Empire; using alternative definitions of Roman towns, which rely on the size of their walled areas or their administrative status during the Roman era; controlling for the distance to Rome and to Scandinavia; or controlling directly for locational fundamentals, and allowing their effect to differ in Britain and France. We also show that our results are not driven by differential changes over time (due to different histories or secular environmental changes) that favoured particular regions within Britain and France. Nor is it the case that Britain's urban locations were perennially less stable than those in France: we find similar locational persistence in Britain and France from the Iron Age to the Roman era and again from the Middle Ages until the Industrial Revolution. Furthermore, we show that our results are not the consequence of differential choice of town locations by the Romans in Britain and France: our findings are similar when we instrument Roman town locations using the locations of major Iron Age settlements. Our results are also not driven by the survival of Roman roads, fortifications, durable masonry, or tombs of late Roman era saints in Britain, since all these actually make the observed persistence of Britain's town locations higher and more similar to France's. Our findings above indicate that the resetting of Britain's urban network allowed it to reconfigure, while France's urban network was largely shaped by its Roman origins. But was this because the Roman locations were still suitable for medieval French towns, or did they become obsolete? Our analysis focuses on a particular dimension of each town's location: its accessibility to transportation networks. During the Roman era roads connected major towns and other towns emerged alongside these roads, since the Roman army (which used the roads to move quickly in all weather conditions) played major economic and administrative roles. But during the Middle Ages, the deterioration of road quality and technical improvements to water transport increased the importance of coastal access. Using estimates from the history literature, we show that this change appears to have been quantitatively important: the cost advantage of water transport over land transport increased considerably from the Roman era to the Middle Ages. In our empirical analysis, we find that during the Middle Ages towns in Britain were roughly two and a half times more likely to have coastal access – either directly or via a navigable river – than during the Roman era. In other words, given a much cleaner slate, British town location responded to the changing value of locational fundamentals. In contrast, in France the weight of Roman history meant that there was little change in the urban network's coastal access over the same period.3 Our finding that Britain's urban network gained more coastal access than France's is not driven by fixed differences in geography. First, our cross‐sectional measure of towns’ coastal access accounts for differences in the proportion of land area with coastal access. This means that we account for fixed differences in the relative abundance of rivers and coasts between Britain and France. Second, we focus not on the cross‐sectional differences between Britain and France but on changes over time in coastal access. Third, the fact that Britain is an island mattered little for the towns that we examine, south of Hadrian's Wall. The medieval seaborne trade of these towns rarely involved circumnavigating Scotland's shoreline. Finally, we show medieval French towns were more likely than their British counterparts to have no coastal access (or poor access) while being within 25 kilometres of locations with coastal access (or with better access).4 These towns therefore had alternative sites nearby with locational fundamentals which would have better served their local markets. But did it actually matter that French towns did not move to locations with better coastal access? We argue that it did, since coastal access provided economic advantages to towns. First, in both Britain and France, towns with coastal access in 1200 grew almost 10% faster per century over the subsequent 600 years. This is a sizeable difference in growth rates, and it is important to emphasise that it holds within France as well as Britain. In other words, our evidence on the mislocation of French towns does not hinge only on comparisons between France and Britain but also on comparisons within France. Second, many canals were dug over this period in both Britain and France to facilitate or improve water transportation.5 The fact that these canals were dug and maintained at great expense shows that water transportation links were highly prized. Finally, among the towns that did not have coastal access in the Middle Ages, being (eventually) connected to a canal was associated with faster long‐term population growth. Our study of path dependence in the location of economic activity is related to the seminal theoretical work on path dependence by David (1985) and Arthur (1994) and to models of spatial agglomeration (Krugman, 1991). One strand of empirical literature (Davis and Weinstein, 2002; Brakman et al., 2004; Beeson and Troesken, 2006; Paskoff, 2008; Miguel and Roland, 2011) shows that local economic activity often recovers quite quickly from calamities of war or epidemics.6 Like these papers, we study the effect of a shock (the collapse of the Western Roman Empire), but one which did not only seriously damage individual towns but actually rendered an entire urban network non‐functional for over a century. Moreover, the shock we investigate wiped out pre‐existing property rights, the role of pre‐existing towns as natural focal points and the possibility of national reconstruction efforts. Our article does not contradict the finding that urban networks generally recover from large scale shocks. But we do show an example of an even more extreme shock, which did lead to urban reconfiguration. Our study is also related to Rauch (1993), Redding et al. (2011) and Bleakley and Lin (2012), who study evidence of path dependence in the location of economic activity, though over shorter time horizons than ours. In Redding et al. (2011), the location into which economic activity is locked in is no worse than the alternatives. The case examined in Bleakley and Lin (2012) is more nuanced: they find that the locations into which economic activity is locked in may have some drawbacks, although they do not quantify their costs. The path dependence that we document is consequential, leaving towns in worse locations than they might have otherwise been in. In this respect, our article is also related to Nunn and Puga (2012), who find that a history of slavery concentrated economic activity in rugged parts of Africa, and Glaeser (2005), who analyses New Orleans as an example of a poorly located city.7 Our study is also related to the research on the economics of the Roman Empire (Temin, 2006, 2012). While some studies (Bowman and Wilson, 2011) examine the patterns of Roman urbanisation, there is much less systematic econometric evidence on the relation of the Roman urban network to later periods. At the same time, existing studies of the role of access to water transportation in the development of European urbanisation (Acemoglu et al., 2005; Bosker et al., 2013; Bosker and Buringh, 2017) typically study the period starting in the Middle Ages. As far as we are aware, ours is the first study, which systematically tracks the location of towns over the course of two millennia.8 The new dataset that we construct is one of our contributions, affording a much longer window into the origins of European urbanisation, from the Iron Age, through the Roman and medieval eras until the present day. A further contribution of our study is its methodology for tracking the persistence of urban locations over time, which allows us to account for the changing role of locational fundamentals. Our findings show that urban networks may reconfigure around locational fundamentals that become more valuable over time. This reconfiguration, however, is not inevitable and towns may remain trapped in bad locations over many centuries and even millennia. This spatial misallocation of economic activity over many centuries has almost certainly induced considerable economic costs. Moreover, the conclusion that cities and towns may be misplaced still matters today, as the world's population becomes ever more concentrated in cities. Parts of Africa, for example, including some of its cities, are hampered by poor access to the world's markets due to their landlocked position and poor land transport infrastructure. And across the world, many cities lie close to areas that are susceptible to flooding, earthquakes, volcanic eruptions and other natural disasters. Our article suggests that policy makers that influence the creation and expansion of towns should be aware that the choices they make may trap people in bad locations for centuries and should take the long‐term consequences of their decisions into account. The remained of this article is structured as follows. Section 2 discusses the historical setting. Section 3 describes the data. Section 4 contains the empirical analysis. Finally, Section 5 concludes.

1 Historical Setting In this Section, we briefly review the early development of towns in the areas that make up present‐day Britain and France during the Roman and early medieval eras. Before the Roman conquest, Celtic tribes using Iron Age technology occupied much of France and Britain.9 Their society was predominantly agrarian, although some economic activity was concentrated in oppida or other settlements, which can be considered proto‐urban (Wacher, 1978; Jones and Mattingly, 1990; Woolf, 1998).10 Rome conquered most of the area that constitutes present‐day France from around 58–50 BCE, under the leadership of Julius Caesar. Rome's conquest of Britain began about one century later, during the reign of the emperor Claudius (from around 43 CE). In both areas, some towns were built for retired soldier‐citizens and others were designated as administrative centres for conquered or client tribes, either on or near the sites of Iron Age settlements or in newly selected locations. Still other towns emerged as civilian settlements around military forts or camps. And other towns emerged primarily to serve economic functions along the roads that were built to connect earlier towns.11 During the first two centuries of the first millennium, many Roman towns in north‐western Europe thrived with long distance trade (Woolf, 1998; Mattingly, 2006; Fleming, 2010). During this period, when the Roman Empire reached its zenith, larger Roman towns in both Britain and France provided a range of private and public services. These towns had markets, workshops, local governance centres, schools, places of worship, entertainment facilities and baths. Smaller towns did not enjoy such a breadth of services but were still places where local non‐agricultural economic activity concentrated. While much information about these towns has been lost to time, existing evidence suggests that the Roman towns in Britain were in many ways similar to their counterparts in France, and especially to those in northern France.12 The third century saw a series of crises throughout the Roman Empire, including the formation of a breakaway Gallic Empire which temporarily ruled most of Britain and France before these territories were brought back into the Roman Empire. The warfare and usurpations were accompanied by a contraction of the towns in France, while the towns in Britain were less adversely affected until the early fourth century (Esmonde‐Cleary, 1989; Faulkner, 2000; Loseby, 2000). Roman Britain's condition at the time is summarised by Ward‐Perkins (2001, p. 350): ‘at least in the early fourth century, the province of Britain was flourishing, with a rich villa economy in the countryside, and a network of towns which included not only administrative capitals (civitates), but also secondary production and marketing centres whose prosperity depended primarily on economic activity’. The years that followed, however, dealt harsh blows to Roman Britain. It suffered incursions of Picts from the north and a series of usurpations and reprisals against its elite, and its economy and towns contracted severely (Mattingly, 2006; Fleming, 2010). Around 410 CE Germanic tribes crossed the Rhine into Gaul and Rome itself was sacked for the first time in centuries. Around that time, the remaining Roman legions left Britain with the last in a series of usurpers (Mattingly, 2006). This was, it appears, one blow too many for an already fragile economy. Palliser (2000, p. 135, quoting Esmonde‐Cleary, 1989), writes that the economy of Roman Britain ‘functioning with difficulty between c. 380 and 410, collapsed suddenly “in the generation or so after 411. In that time the towns, the villas, the industries and the other material evidence diagnostic of Roman Britain disappeared”’. Other researchers reach similar conclusions. Fleming (2010, p. 28) writes that ‘At some point in the early fifth century, though, urban life died completely, and all of Britain's towns, public and small, simply ceased to exist’. In other words, the towns in Britain collapsed before the arrival of the Anglo‐Saxons, and as Mattingly (2006, p. 533) writes, ‘It now seems clear that there was no real continuity of urban community between Roman Britain and Saxon England’. In the ensuing centuries political control in Britain became highly fragmented; the use of coins and trade in bulky items such as pottery was discontinued (Fleming, 2010); and the Church of Rome lost control until around 597 (Loseby, 2000). As Ward‐Perkins (2001, p.361) writes, ‘Post‐Roman Britain, of the fifth and sixth century, retained almost nothing of the sophistications of Roman economic life and, although this is a fact that is initially hard to credit, even sank to an economic level well below that reached in the pre‐Roman Iron Age’. In the agricultural economy that remained in Britain there was no room for towns. In a recent quantitative analysis, Faulkner (2000) estimated the number of rooms occupied in private buildings in 16 major Roman‐British towns. He found that this number increased from the Roman invasion of Britain until around 200 CE, and thereafter remained stable for about a century. The number of rooms then fell by around 90% from the first quarter of the fourth century to the first quarter of the fifth century and, by the middle of the fifth, it fell to zero. It is important to emphasise that even important Roman towns in Britain, which re‐emerged much later as urban centres, including Londinium (London), Venta Belgarum (Winchester), Durovernum Cantiacorum (Canterbury) and Eboracum (York), were abandoned before being reoccupied during the Middle Ages.13 In France, meanwhile, the Western Roman Empire also struggled and eventually collapsed, and Germanic tribes (Franks) seized control. But in France these tribes were soon unified under the Merovingian Dynasty, which controlled most of France from the sixth century until the eighth century (Wickham, 2009). So France, unlike Britain, experienced much less political fragmentation. Under its Christian Merovingian rulers, the Roman church continued to play important roles; legal practices were not abandoned; coin use continued; and the economy, unlike Britain's, did not fail (Nicholas, 1997; Wickham, 2005; Ward‐Perkins, 2006). Fleming (2010, p. 71) describes fifth‐ to early seventh‐century Gaul: ‘many components of Roman culture and economy persevered here, in ways that they did not in Britain. Indeed, not only did written administration and the state survive, but so too did old Gallo‐Roman elite families … a money economy and towns. Even vestiges of Roman modes of industrial‐scale production were present … The Franks … produced copious amounts of jewellery, gold coins, wine, ceramics and textiles’. In these circumstances, as Nicholas (1997, p. 23) writes, ‘Although Roman urbanisation … virtually ended in Britain … a stronger case for continuity can be made for some cities of interior Gaul, particularly those that housed bishoprics’. In summary, the urban networks in Britain and France, which had many similarities during centuries of Roman rule, experienced different fates when the Western Roman Empire fell. While the urban network of Britain was effectively reset by 450 CE and only started to recover after 600 CE, the urban network in France contracted but, for the most part, remained intact.

2 Data Description In this Section, we briefly describe the data that we use in our empirical analysis, leaving a more detailed description to online Appendix B. We construct our dataset around a grid of points, which allows us to consider all potential locations for towns within the areas we analyse. The small size of the squares of our grid, each covering 1 kilometre2, enables us to differentiate locations that are close by and yet differ in their fundamentals or in their urban histories.14 As we explain below, we associate each town with a gridpoint, which approximates the location of the town centre. We take this approach mostly because of the impracticality of tracing the way in which towns areas have changed over time. In our empirical analysis, we typically allow for 5 kilometre bands around locations, to account for possible measurement error. Using a geographic information system (GIS), we begin with a grid that covers the entire land area of the Roman Empire at the time of its greatest extent, around the death of Emperor Trajan in 117 CE.15 At the time the Roman Empire had a land area of about 5 million kilometre2 (Taagepera, 1979), mostly around the Mediterranean and parts of Western Europe. We focus most of our analysis on Britain (as far north as Hadrian's Wall) and France, which had similar histories during the Roman and Norman eras. In some of our robustness checks we also use data on all the north‐western provinces of the Roman Empire, which presently lie within the United Kingdom, France, Belgium, Luxembourg, the Netherlands, Germany and Switzerland.16 To this grid we add, using GIS, data on a number of locational fundamentals. We compute a measure of elevation in metres using a 3 × 3 kilometre2 grid of elevation (ESRI, 2010). Using these elevation data, we also compute a measure of ruggedness, following Nunn and Puga (2012) and Riley et al. (1999). The summary statistics for these and our other variables are reported in Table 1. Table 1. Summary Statistics Variable Full sample (906,075 observations) Britain and France only (697,198 observations) Mean SD Mean SD Britain indicator 0.16 0.37 0.21 0.41 France indicator 0.61 0.49 0.79 0.41 Elevation (meters) 350 433 296 377 Ruggedness 446 540 462 535 Coast within 5 kilometres 0.05 0.22 0.06 0.24 Coastal access I 0.11 0.32 0.14 0.34 Coastal access II 0.20 0.40 0.25 0.43 Suboptimal location I 0.26 0.44 0.32 0.46 Suboptimal location II 0.38 0.49 0.47 0.50 Pre‐Roman origins 0.00010 0.00997 0.00013 0.01136 Iron Age settlement 0.00017 0.01295 0.00019 0.01376 Belgica indicator 0.10 0.30 0.09 0.28 Lugdunensis indicator 0.18 0.38 0.23 0.42 Roman road within 1 kilometre 0.17 0.37 0.17 0.37 Roman town (baseline) 0.00027 0.01631 0.00035 0.01859 Roman town with 5+ hectare defences 0.00012 0.01082 0.00014 0.01173 Roman administrative town 0.00017 0.01320 0.00019 0.01386 Roman bishopric in the fourth century 0.00010 0.00985 0.00013 0.01123 Bishopric (or archbishopric) between 700 and 900 0.00016 0.01252 0.00018 0.01323 Mint between 768 and 1066 0.00020 0.01421 0.00023 0.01524 Town with 1k+ population between 1086 and 1200 0.00022 0.01467 0.00019 0.01381 Town with 5k+ population in 1200 0.00013 0.01146 0.00011 0.01051 Town with 5k+ population in 1300 (Russell) 0.00009 0.00951 0.00008 0.00872 Town with 5k+ population in 1300 0.00011 0.01051 0.00007 0.00830 Largest 50 towns 1377–1400 0.00011 0.01051 0.00014 0.01198 Town with 10k+ population in 1400 0.00015 0.01216 0.00009 0.00958 Town with 5k+ population in 1500 0.00018 0.01329 0.00012 0.01084 Town with 5k+ population in 1600 0.00028 0.01667 0.00024 0.01552 Town with 5k+ population in 1700 0.00035 0.01858 0.00031 0.01748 Town with 10k+ population in 1700 0.00015 0.01207 0.00012 0.01104 Town with 5k+ population in 1800 0.00068 0.02598 0.00061 0.02462 Town with 10k+ population in 1800 0.00024 0.01551 0.00022 0.01491 Town with 10k+ population in 2012 0.00323 0.05674 0.00250 0.04998 Town with 20k+ population in 2012 0.00176 0.04191 0.00138 0.03708 Town with 50k+ population in 2012 0.00051 0.02255 0.00043 0.02070 Town with 100k+ population in 2012 0.00018 0.01357 0.00014 0.01204 2010 2013 ( i ) the coast or a (narrowly defined) navigable river, which flows into the ocean or a sea (‘Coastal access I’); or

the coast or a (narrowly defined) navigable river, which flows into the ocean or a sea (‘Coastal access I’); or (ii) the same, except using a broader definition of navigable rivers (‘Coastal access II’).17 We also calculate the closest distance from each grid point to the coast (using ESRI,) and to the nearest navigable river (using Historical GIS for European Integration Studies,). This allows us to construct indicators for whether each gridpoint is within 5 kilometres of: Having discussed the measurement of the terrain, we now describe how we measure towns.18 Our main source of data on modern towns (including cities) is the World Gazetteer (2012), which compiles population data from official national statistical agencies.19 Based on these official data, the website provides an estimate of each town's 2012 population. We focus our analysis of modern towns on those with estimated populations of 10,000 or more in 2012. We use the World Gazetteer, complemented by other sources, to identify each town's coordinates and we assign each town to its nearest grid point. We then use the grid with the modern towns as the basis for matching in earlier towns and sites, most of which are identified by name and approximate location, from a variety of sources, as we discuss in more detail in online Appendix B. In reconstructing the historical populations of towns we use, like many researchers before us, the estimates of Bairoch et al. (1988). Unfortunately, this source covers French towns from 800 CE and Britain towns only from 1000 CE, so in order to look further back in time we require other data.20 In tracing the origins of western European urbanisation back into the first millennium, we tried to balance a number of criteria. First, we wanted measures that capture the spatial concentrations of economic activity, which typically characterise towns. Second, we sought where possible to obtain estimates made in recent years, reflecting knowledge that has been built up by historians and archaeologists. Third, we looked for town definitions that were as comparable as possible for the areas that make up present‐day Britain and France. Fourth, when considering post‐Roman urbanisation in particular, we searched for measures of urbanisation dating back as early as possible, even if in some cases the locations were at the time only proto‐towns and not fully fledged ones. Finally, wherever possible, we aimed for definitions that covered more than a handful of sites in both Britain and France, to facilitate a meaningful statistical analysis, starting with the pre‐Roman era. Some scholars (Wacher, 1978; Woolf, 1998) conclude that pre‐Roman north‐western Europe was largely a pre‐urban world. Nevertheless, this world, which was largely populated by Celtic tribes, had some settlements with features that we might recognise as urban (or proto‐urban), such as coin use. To capture the location of the main pre‐Roman settlements, we use data from Fichtl (2005) on Iron Age oppida. This source lists 107 oppida in France but only 11 oppida in Britain, so we also use Jones and Mattingly (1990) to locate other important Iron Age settlements in Britain, which may be seen as harbingers of British urbanisation. In measuring Roman‐era towns, we face the challenge that different authors define Roman towns differently and arrive at different lists of towns. To mitigate this problem, we do not rely on just one particular definition a ‘Roman town’ but instead use three different definitions. Our first (baseline) measure is an indicator for Roman towns using classical references: Wacher (1995) for the main towns of Britain, Burnham and Wacher (1990) for the ‘small towns’ of Britain and Bedon (2001) for Roman towns of various sizes in France.21 These sources, which describe the archaeology of each town in some detail, reveal many similarities between the Roman towns in Britain and France, as one might expect from neighbouring areas within the empire. In particular, larger Roman towns in both Britain and France had civil, commercial and residential buildings that served a broad range of economic functions, whereas smaller towns typically had a more limited range of buildings, mostly residential and commercial. As online Appendix Table A1 shows, our baseline sample includes 74 Roman towns in Britain and 167 Roman towns in France. Panel (c) of the Table also reports separately the number of Roman towns in northern France, defined using the two Trajan provinces of the Roman Empire (Belgica and Lugdunensis). The Table also shows that the Roman towns in Britain were quite similar to their counterparts in France in their origins (pre‐Roman or Roman) and their coastal access, although towns in France were generally located in higher elevations and in more rugged terrain.22 Our empirical methodology (below) allows us to control for pre‐existing differences in locational fundamentals. Our second measure of towns uses the size of walled (defended) areas of towns. Since precise population estimates for towns are unavailable, researchers often use these walled areas to construct population estimates.23 We apply a common quantitative criterion – at least 5 hectares of walled area – for selecting Roman towns across north‐western Europe. When using this approach, like the one above, we still focus on Roman towns, as opposed to garrison forts that did not develop into towns (such as Chester). This approach has advantages but also its limitations: some Romans lived outside town walls (Goodman, 2007); within the walls population densities may have differed; and some important Roman towns, especially in France (e.g. Marseille) did not have town walls. Nonetheless, this approach provides a useful complement to our baseline definition of Roman towns.24 Each of these towns probably housed at least 500–1,000 people and at most tens of thousands of people (Bowman and Wilson, 2011). As Table A1 shows, Roman towns with walled areas of five hectares or more number 38 in Britain (with an average log walled area in hectares of 2.93) and 58 in France (with an average log walled area in hectares of 2.96), of which 30 are in northern France (with an average log walled area in hectares of 2.78). The similarity of these figures suggests that in terms of their population, the towns of Roman Britain were not too dissimilar from those of France. Moreover, a comparison of the walled areas of Roman towns in Britain and northern France suggests that it is highly improbable that urbanisation survived in northern France and not in Britain because Britain's towns were vastly inferior. While defence was important for many Roman towns, we wanted to focus our study on sites that had an urban character, not on military camps. For this reason, we did not rely on the Barrington Atlas of the Greek and Roman World (Talbert, 2000), whose classification of sites by importance does not correspond closely with urbanisation. For example, two of the major sites that it reports for Britain (one in present day Chester and the other in Scotland) appear to correspond to Roman military camps without much civilian urbanisation. We also note that among the Roman military sites reported in Åhlfeldt (2015), the smaller camps are generally located away from key areas of Roman urbanisation, such as the South of France and the south of Britain. And the legionary camps reported in Åhlfeldt (2015) also generally do not overlap with the Roman towns we study, with only two exceptions in Britain and one in France. Our third and final definition of Roman towns relies on the administrative classifications of the Romans themselves. Each Roman administrative town was classified as either colonia, municipium or ‘civitas capital’ (Mattingly, 2006 for Britain and Bedon, 2001 for France). These administrative designations became less important over time and they imperfectly captured towns’ evolving size and economic importance. As we discuss in online Appendix B, these measures are also more problematic for Roman Britain. We therefore use them only in a limited number of robustness checks. In total our data set includes 24 administrative Roman towns in Britain and 110 in France, of which 46 are in northern France (as defined above). We complement the data on the location of Roman towns using these three definitions with additional information. We use data from Bedon (2001) to identify Roman towns that had bishops in the fourth century.25 To identify whether the Roman towns had pre‐Roman origins, we use Millett (1990) for Britain and again Bedon (2001) for France.26 During its post‐Roman period, from 450–600 CE, Britain had no functional towns (as discussed in Nicholas, 1997; Palliser, 2000; Ward‐Perkins, 2001; Mattingly, 2006; Fleming, 2010), while in France many towns survived. From the seventh century onwards, trading settlements known as emporia (or ‘wics’) began to emerge in Britain (Fleming, 2010). These emporia had some urban features (and are sometimes described as ‘proto‐urban’), although they were typically undefended. Only few such sites have been identified in Britain, however, and they have almost no counterpart in France (Quentovic being a rare exception), making a quantitative analysis impractical.27 Our first measure of post‐Roman urbanisation identifies the seats of bishops (including archbishops), known as bishoprics, from 700 to 900 (Reynolds, 1995). From these locations bishops, exercised power at a time when the church was central to many aspects of life. The bishops and their followers also produced and consumed various products and services, sustaining a spatial concentration of economic activity (Nicholas, 1997; Fleming, 2010). The bishoprics thus provide a window into early post‐Roman (proto) urbanisation. Our next measure of (proto) urbanisation is more directly related to the location of economic activity in early medieval Europe, namely the minting of coins. While the size and importance of early mints varied considerably, their presence suggests a concentration of local economic activity for a period where good measures of economic activity in both Britain and France are difficult to come by. We use data from Spufford (1988), who describes the location of mints in Carolingian and post‐Carolingian France and in pre‐Norman Britain (from 768 to 1066). The main advantage of the bishoprics and the mints is that they allow us to trace the early stages of urban recovery in post‐Roman Britain and France. For later years, however, we have more direct and conventional measures of urban activity in the form of population estimates. As discussed above, Bairoch et al. (1988), which is a standard reference, reports town population estimates for Britain only from 1000 onwards and, in the first few centuries of the second millennium, the number of British towns it covers is low compared to the numbers discussed in Holt (2000). Given our focus on the location of towns, albeit small, we construct an indicator for towns with 1,000 people or more in Britain or France, using any town with estimated population in this range from Bairoch et al. (1988) for 1000–1200 or Dyer (2000), which provides estimates based on the Domesday Book. While this approach has its drawbacks (it may, for example, miss small towns in France if they are excluded from Bairoch et al., 1988) it permits a quantitative analysis of the location of early towns in both Britain and France. Despite its limitations, Bairoch et al. (1988) is our main source for the population of towns for each century from 1200 to 1800. Because of the selection problems related to smaller towns, we focus on towns with at least 5,000 inhabitants. Since town populations grew rapidly during the Industrial Revolution, we use an additional population threshold of 10,000 inhabitants or more for towns in 1800. Because the medieval era is important for our analysis, we also use Russell (1972) as an alternative estimate of town populations circa 1300, before the onset of the Black Death. From Russel's estimates, we again construct an indicator for towns with 5,000 people or more, as we do using the estimates of Bairoch et al. (1988) for that period. For the period following the Black Death, we construct an indicator for the 50 most populous towns in Britain and France. This measure takes the largest 50 towns as reported by Bairoch for 1400 and adds the 50 largest town in Britain as measured by the number of taxpayers based on the poll taxes of 1377–1381, as reported in Dyer (2000).28 While the size of towns included in this measure most likely differs between Britain and France, this measure helps us understand the location of towns up to a fixed threshold in the town size hierarchy. Finally, to examine individual towns that are locally important, irrespective of their absolute or relative size within a country, we compute arbitrary grid cells of 100 × 100 kilometre2 using an equal area projection in GIS. We then compute indicators for the largest towns within each of these cells for each century from 1200 to 1800 (using Bairoch et al., 1988) and for 2012 (using the World Gazetteer, 2012). We also use these same cells to cluster the standard errors in our analysis below.

3 Empirical Analysis 3.1 Measuring the Persistence of Town Locations To motivate our empirical analysis, we present in online Appendix A a simple model of town location. This model allows for possible changes in first‐nature locational fundamentals (or their value) and also for shocks that could destroy the towns, such as the one experienced by the ending of Roman Britain. This model allows for different possible scenarios. In Scenario 1, locational fundamentals consistently favour a particular location. Here, even if a shock destroys the town, it will form again in the same location. In Scenario 2, first‐nature locational fundamentals (or their value) change over time and the town follows. In Scenario 3, even if first nature fundamentals or their value change, the town persists in its location for historical reasons – in the model it is held in place by agglomeration but in reality this may be reinforced by the value of past sunk investments. In this case, a shock that ends the town will lead to its re‐formation in a different location – the one with improved fundamentals. There are two variants to this third scenario: differences in first nature fundamentals may be relatively small and inconsequential; or they may be large but not large enough to shift the town unless it is exogenously destroyed. Before proceeding with the econometric analysis of these possible scenarios, we begin our examination of the persistence of town locations from the Roman era by examining the data visually. Panel (a) of Figure 1 shows the location of the baseline Roman towns in present‐day Britain and France. The other three panels of the Figure compare the locations of these towns to our three earliest measures of urbanisation (or proto‐urbanisation) in the post‐Roman early medieval era, starting with the medieval bishoprics. Historians have commented on the spatial reallocation of power centres, both secular and ecclesiastical, in post‐Roman Britain.29 Loseby (2000) discusses the efforts of Pope Gregory I to bring Britain back into the fold of the Roman Church in the late sixth century. The old Roman towns seemed like natural targets for the early missionaries but in many cases the location of power centres had already shifted by 600 CE and the location of the newly established bishoprics had to adjust to the new reality. And as panel (b) of Figure 1 shows, the location of Bishoprics (including Archbishoprics) from 700 to 900 in Britain appears to differ from the location of Roman towns much more than it does in France. Figure 1 Open in figure viewer PowerPoint Towns in Roman and Medieval Times. Panel (a): Roman Baseline Towns ( ); Panel (b): Roman Baseline Towns ( ) and Medieval Bishoprics and Archbishoprics (8th and 9th century, ); Panel (c): Roman Baseline Towns ( ) and Medieval Mints (768–1066, ); Panel (d): Roman Baseline Towns ( ) and Medieval Towns (1086–1200, ) Notes. The maps show the location of all the Roman Baseline Towns in our dataset and the location of later towns as specified in each panel for the Roman parts of Britain and France. See the data section for sources and definitions of towns. Colour figure can be viewed at wileyonlinelibrary.com. The location of economic activity in early medieval Britain, as reflected (admittedly imperfectly) by the location of pre‐Norman mints, tells a similar story. The locations of coin mints in Britain bear relatively little resemblance to the location of Roman towns, unlike their counterparts in France. Finally, in the early Norman period, the location of towns with 1,000 people or more from 1086 to 1200 in Britain is again quite different from the location of Roman towns, while in France there is much more locational persistence. Online Appendix Figure A1 shows comparisons of the locations of Roman towns with defended areas of 5 hectares or more to early medieval towns, and once again we see more persistence in France than in Britain. The maps also show that the difference in persistence of town locations is not driven by differences in the number of towns (in absolute terms or relative to land area) between Britain and France. For example, early bishoprics are rarer in Britain, while coin mints are far more common. This is noteworthy for our empirical analysis below, since the number of larger towns (with 5,000 people or more) was lower in Britain compared to France for a long time after the collapse of Roman Britain. While these measures of towns during the Middle Ages are admittedly imperfect, we prefer them, especially the population estimates of towns from 1086 to 1200, to the more precise population figures from later years. This is because as we move beyond the Middle Ages, England become the preeminent maritime power and this could have affected the differences in its outcomes compared to France. Nevertheless, we note that the differences in persistence between France and Britain lasted for many more centuries. As Table A2 shows, the difference in persistence of town locations compared to the Roman era continued through to 1700, around the eve of the Industrial Revolution, when only five of the largest 20 towns in Britain were within 5 kilometres of Roman town sites, compared to 16 in France (and 13 in the northern parts of France, covering the Roman provinces of Lugdenensis and Belgica). The picture today is still strikingly similar: only two of the top 20 British towns are located near Roman town sites, compared to 16 in France as a whole (and still 13 in northern France, as defined above).30 i) to estimate the following specification for various time periods (indexed by t): (1) is an indicator for being close (within 5 kilometres) to later (medieval or modern) town; is an indicator for the site of a settlement, in this case a Roman‐era town; is and indicator for Britain; and is an error term. (2) for France and for Britain and test the null hypothesis that these ratios are equal, as predicted by Scenarios 1 and 2, against the alternative that the ratios are different, as predicted by Scenario 3. Having examined the data, we now conduct more formal empirical tests of the persistence of town locations in Britain and France. We use a cross section of grid points (indexed by) to estimate the following specification for various time periods (indexed by):whereis an indicator for being close (within 5 kilometres) to later (medieval or modern) town;is an indicator for the site of a settlement, in this case a Roman‐era town;is and indicator for Britain; andis an error term. 31 This specification allows us to calculate the probability that a site with (and without) a Roman town is used by a later town in both Britain and France. Specifically, we calculate the following odds ratio:where ‘used by’ denotes proximity (within 5 kilometres in the baseline specification) and here ‘early town’ denotes a Roman town, and ‘later town’ denotes a number of measures of towns in the post‐Roman era. We calculate this odds ratio because the spatial density of later towns differs by country over time; when the network is denser there is a higher probability that later towns might be located near Roman town sites purely by chance. The odds ratio accounts for this by normalising by the probability that a non‐Roman town site is correspondingly more likely to be near a later town. 32 We calculate the odds ratio asfor France andfor Britain and test the null hypothesis that these ratios are equal, as predicted by Scenarios 1 and 2, against the alternative that the ratios are different, as predicted by Scenario 3. 33 As Table 2 shows, for many different measures of towns (and proto‐towns) from 700 to 1700, the persistence measured by the odds ratio is around 7–13 in Britain, or about three times smaller than in France (where the odds ratio is around 20–40). The tests reject the equality of the odds ratios, consistent with the predictions of Scenario 3, where the persistence of town locations is high in France and lower in Britain. This holds both in cases where there are fewer later towns per kilometre2 in Britain than in France (as in the case of the medieval bishoprics) and in cases where the opposite is true (as in the case of medieval mints).34 The Table also shows that using correlations instead of odds ratios yields similar results, although we prefer the odds ratios approach, which allows us to add regression controls, as we explain below. Table 2. Probability of Towns (700–2012) within 5 kilometres of Roman Towns Bishopric or arch‐bishopric in 700–900 Coin mint in 768–1066 Town with 1k+ people in 1086–1200 Town with 5k+ people in 1200 Town with 5k+ people c. 1300 (Russell) Town with 5k+ people in 1300 One of largest 50 towns in 1377–1400 Town with 5k+ people in 1400 Town with 5k+ people in 1500 Roman town 0.566 0.343 0.365 0.279 0.234 0.162 0.203 0.203 0.225 (0.041) (0.041) (0.041) (0.036) (0.032) (0.027) (0.033) (0.033) (0.032) Britain −0.006 0.031 0.012 −0.001 −0.000 −0.000 0.018 −0.001 0.001 (0.002) (0.008) (0.003) (0.002) (0.002) (0.002) (0.004) (0.002) (0.002) Roman town × Britain −0.466 −0.114 −0.159 −0.205 −0.185 −0.127 −0.012 −0.141 −0.14 (0.054) (0.062) (0.058) (0.046) (0.043) (0.034) (0.052) (0.044) (0.051) Intercept 0.015 0.011 0.012 0.009 0.006 0.005 0.007 0.007 0.009 (0.002) (0.001) (0.002) (0.001) (0.001) (0.001) (0.001) (0.001) (0.001) Ratio Britain 13.12 6.52 9.79 10.93 9.78 8.08 8.62 10.93 9.91 Ratio France 39.58 33.32 31.81 33.25 41.03 31.75 30.90 29.68 27.38 Ratio Britain/France 0.33 0.20 0.31 0.33 0.24 0.25 0.28 0.37 0.36 p‐value* 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.003 0.001 Correlation Britain 0.025 0.026 0.030 0.019 0.015 0.011 0.027 0.017 0.019 Correlation France 0.082 0.058 0.059 0.052 0.053 0.039 0.043 0.042 0.043 Town with 5k+ people in 1600 Town with 5k+ people in 1700 Town with 10k+ people in 1700 Town with 5k+ people in 1800 Town with 10k+ people in 1800 Town with 10k+ people in 2012 Town with 20k+ people in 2012 Town with 50k+ people in 2012 Town with 100k+ people in 2012 Roman town 0.365 0.432 0.249 0.564 0.352 0.542 0.504 0.298 0.169 (0.037) (0.040) (0.031) (0.033) (0.038) (0.037) (0.039) (0.038) (0.029) Britain −0.000 −0.001 0.001 0.016 0.013 0.2 0.135 0.065 0.024 (0.003) (0.004) (0.002) (0.007) (0.005) (0.026) (0.023) (0.012) (0.004) Roman town × Britain −0.248 −0.292 −0.191 −0.364 −0.23 −0.249 −0.234 −0.107 −0.076 (0.062) (0.055) (0.041) (0.052) (0.051) (0.070) (0.075) (0.060) (0.047) Intercept 0.018 0.023 0.009 0.04 0.013 0.074 0.041 0.013 0.005 (0.002) (0.002) (0.001) (0.003) (0.001) (0.009) (0.006) (0.002) (0.001) Ratio Britain 7.53 7.42 7.01 4.55 5.62 2.07 2.54 3.44 4.15 Ratio France 21.17 19.69 29.47 15.00 28.06 8.28 13.42 23.83 33.83 Ratio Britain/France 0.36 0.38 0.24 0.30 0.20 0.25 0.19 0.14 0.12 p‐value* 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 Correlation Britain 0.020 0.021 0.013 0.019 0.017 0.015 0.016 0.016 0.012 Correlation France 0.048 0.050 0.046 0.050 0.054 0.036 0.044 0.046 0.041 We conduct a number of checks to show the robustness of the findings described in Table 2. Panel (a) of online Appendix Tables A3 and A4 shows that the results hold when we expand the measure of proximity from 5 to 10 kilometres. We note that these 10 kilometre bands cover an area of over 300 kilometre2 closest to each grid point. Panel (b) shows results from specifications with a narrower definition of proximity, looking only at whether the same point was used by towns in different periods, and again the differences between Britain and France are large and significant.35 In panel (c) we restrict the area in France to its northern regions, which are more similar to Britain, and again our estimates are very similar to the baseline. In panel (d) we use the same specification as in our baseline but this time using only Roman towns with defended areas of 5 hectares or more; again the differences between Britain and France are similar and, perhaps, even slightly starker. Panel (e) uses the same definition of towns as panel (d) but expands the geographical coverage to all the parts of the Roman Empire in north‐western Europe; the results are again similar to the baseline. Panel (f) is the same as the baseline but this time using only Roman administrative towns. Here the differences between Britain and France are still mostly significant, although not in all cases, perhaps because only 24 Roman towns in Britain are known to have had an administrative status. Panel (g) restricts the baseline Roman towns to those with pre‐Roman origins, with results that are similar to the baseline. This shows that our results are not driven by the Romans’ decision to locate some towns in previously unsettled sites, which may have potentially differed in present‐day Britain and France. Finally, panel (h) uses the same specification as in the baseline, except that now we control directly for measures of locational fundamentals and allow their effects to differ in Britain. Our findings are again similar, and perhaps even stronger, showing that the higher persistence of town locations compared to the Roman era in France is not driven by differences in observed locational fundamentals.36 One particular concern is that Roman town sites in Britain may have remained locally important even if they declined in absolute size along with their local economy. This may affect our results on persistence if changes in climate or technology during the medieval era favoured areas in Britain that had few Roman towns, while perhaps inducing less regional change in France. A casual inspection of Figure 1, however, suggests no marked shift in the regional concentration of towns in Britain, with towns remaining more concentrated in southern England and the Midlands than in northern England and Wales. Nonetheless, to address the concern that regional reallocation may affect our results, we estimate specifications similar to those above, using as outcomes indicators for the largest town in each 100 × 100 kilometre2 cluster in different points in time. The results in Table A5 show that even using this measure the persistence of town locations is lower in Britain than in France. As before, restricting the areas in France to its northern regions leaves the picture essentially unchanged.37 One potential concern for our identification strategy is that Roman choice of town locations may have, perhaps for military reasons, differed in Britain and on the continent. We already saw that our findings were robust to using only towns with pre‐Roman origins, but again one might be concerned that the Romans only selected to build towns on certain pre‐existing settlements. To address this concern we use major pre‐Roman Iron Age settlements as an instrument for Roman town location. This approach relaxes the assumption that the Romans chose town sites in a similar way in Britain and France. It does, however, assume that Iron Age sites were more likely to serve medieval or later towns only because they also served Roman towns. If some Iron Age sites became medieval towns because they provided refuge for people in the volatile post‐Roman era, this might result in 2SLS estimates that are larger than the OLS estimates, especially in Britain, where the collapse was more severe. To construct our instruments, we first identify the location of important Iron Age settlements known as oppida (Fichtl, 2005). As we discuss above, these were focal points for economic activity, typically with some defences, which existed prior to the Roman conquest. As column (1) of Table A6 shows, the location of oppida is a good predictor of the location of Roman towns in France. But as column (2) shows, the statistical power of oppida in predicting town locations in Britain is weaker, probably because there were only 11 oppida in Britain. We therefore also use data on the location of a broader set of major Iron Age settlements in Britain (Jones and Mattingly, 1990). As columns (3) and (4) of Table A6 show, these have stronger predictive power for the location of Roman‐era towns in Britain. We use the location of Iron Age settlements from Fichtl (2005) and Jones and Mattingly (1990) as excluded instruments for and .38 The 2SLS estimates in Table A7 show higher persistence than the OLS estimates, perhaps for the reasons discussed above. The persistence of town location is still higher in France than in Britain, although the estimates are noisier and the ratios are significantly different from each other only in seven out of 12 of the cases. Across all town measures from 700 to 1700, the ratio of ratios (Britain's divided by France's) averages around 0.36, compared to an average of 0.3 in the OLS estimates above. Overall, then, these results suggest that the difference in persistence of town locations from the Roman era is not driven by differences in locational choices made in the Roman era. Another question we examine is whether Britain's urban network showed locational persistence that is similar to France's in periods when neither underwent a shock as severe as Britain did when the Western Roman Empire fell. To examine this, we estimate specifications as in 1 using an indicator for towns with 5,000 people or more in 1200 instead of Roman towns. The results, reported in Table A8, show similar persistence in town location in Britain from 1200 until 1700, around the dawn of the Industrial Revolution.39 Similar tests comparing the locations of Iron Age settlements and Roman baseline towns (available from the authors on request) likewise show similar persistence in both countries. Therefore, were it not for the collapse of Britain's towns during the fall of the Western Roman Empire, we might have expected the persistence of its town locations to have been similar to France's. Our econometric analysis of town locations builds on the work of many historians and archaeologists, who have rigorously pieced together a picture of the Roman urban network. Nevertheless, one potential concern is that we might be unable to account for some Roman towns that are now lost. This concern is probably more applicable to Britain, because there is more written evidence for France (see online Appendix B for further discussion). Since archaeological evidence on Roman towns often comes up incidentally during excavations, which are more common in present‐day towns than in rural areas, any Roman towns that we may be missing are most likely Roman towns in Britain on whose sites no later towns developed. This type of measurement error, if present, would therefore cause us to understate the differences in persistence of urban locations between France and Britain. While we find that the persistence of Roman‐era town locations is low in Britain (compared to France) this persistence is still significantly larger than 1 in most of our estimates. But is this necessarily because locational fundamentals attracted population long after the Roman town ceased to function? In evaluating the persistence of Roman town sites in Britain, we should consider other reasons, besides than natural advantage, which attracted population back to some sites. First, in some cases non‐urban populations continued to dwell in the former Roman towns (Wacher, 1995). Second, some of the roads built by the Romans, and which connected their towns, survived to serve the Anglo‐Saxons (Fleming, 2010).40 Third, some Roman walls survived and were put into use many centuries later, as in the case of medieval London.41 Fourth, even when buildings and walls were no longer serviceable after centuries of dereliction, they sometimes still provided usable masonry. Finally, some Roman towns, which were home to early Christian saints, later became medieval pilgrimage sites, which sometimes developed into towns.42 All these considerations suggest that if the towns of Roman Britain had been wiped out without leaving any trace, the locational persistence of towns in Britain from the Roman era onwards may have been even lower than our estimates suggest. By the same token, the persistence of town locations in France may have been much more than three times higher than in Britain if persistence in Britain had been driven only by natural features, such as rivers and coasts. This consideration is also important when comparing our findings to other recent studies of persistence in modern cities that suffered devastating shocks (Davis and Weinstein, 2002). Modern cities subjected to these shocks may have subsequently attract population because of their cultural legacies, or because they were part of transport networks. Moreover, when modern towns are devastated, property rights for land may attract population even when buildings are destroyed; but in post‐Roman Britain property rights from the Roman era were no longer upheld (Wickham, 2005). Thus, there is reason to believe that the success of cities in recovering from war or outbreaks of disease may not be driven only by their favourable geographic location. 3.2 Why Britain's Urban Network Reconfigured But why did Britain's urban network, which was reset by the fall of the Roman Empire, reconfigure around a different set of locations than its Roman predecessor? We argue that medieval British towns formed in locations that had become more productive in that era, compared to the Roman era. Our empirical analysis below focuses on a particular locational advantage, which is related to the changes in trade costs over time. During the Roman era, the Roman army played an important role in administrating and securing the north‐western parts of the Roman Empire. The Roman army was instrumental in procuring taxes – both in kind and in currency – and in buying locally produced goods and services. The Roman army needed good roads in order to move swiftly and reliably in all weather conditions, so the Romans built an extensive road network to connect the urban networks in present‐day France and Britain. The Romans did, of course, use water transport, but mostly in and around the Mediterranean. In contrast, the North Sea and the English Channel were viewed as more hazardous and their use was more sporadic (Morris, 2010). While a few Roman towns in Britain and France did serve as ports, most towns served local markets. For these towns, which serviced nearby locations, being away from the coast may have actually been advantageous, allowing them to serve larger land areas within a given Euclidean distance. Rivers were important for many Roman towns, providing them with water for consumption and manufacturing, fishing opportunities and, in some cases, serving as a defensive barrier (Nicholas, 1997).43 But most of these benefits could be derived from non‐navigable rivers or other water sources (sometimes using aqueducts) and many Roman towns developed without coastal access.44 In the Middle Ages, the importance of water transportation increased compared to land transportation in present‐day Britain and France, for two different reasons. First, the quality of roads in the medieval era was typically worse than in the Roman era.45 Second, the shallow draft of Norse‐designed ships allowed these ocean‐going vessels to travel on inland waterways (Brøgger and Shetelig, 1971), which may have reduced trans‐shipment costs. For a while, this new technology also made locations with coastal access more vulnerable to Viking raids. By the late eleventh century, however, the Normans controlled most of Britain and France, and raids were no longer a major problem. Comparing the cost advantage of water transport over land transport over time is an imprecise exercise. Still, Scheidel and Meeks (2013) estimate that during the Roman era, land transport may have been, on average, around six times more expensive than river transport. In contrast, Jones (2000) discusses river navigation in England around 1300 and concludes that ‘carriage by land could be more than ten times the price of transport by water’.46 We have no similar quantitative evidence for medieval France but it seems likely that its relative costs would have been similar. All this suggests that coastal access would have been more important for towns during the High Middle Ages than during the Roman era.47 We now examine whether the growing importance of water transportation shifted the urban networks towards locations with coastal access. As Figure 2 shows, approximately half of the baseline Roman towns in both Britain and France had some coastal access. By 1086–1200, however, over three‐quarters of British towns had coastal access, while in France still only about half did.48 Online Appendix Figure A2 shows a similar comparison, with similar results, using only the Roman towns with defended areas of 5 hectares and the medieval towns.49 Figure 2 Open in figure viewer PowerPoint Towns Within and Without Coastal Access. Panel (a): Roman Baseline Towns in Britain; Panel (b): Medieval Towns (1086–1200) in Britain; Panel (c): Roman Baseline Towns in France; Panel (d): Medieval Towns (1086–1200) in France Notes. The Figures show shaded areas that are within five kilometres of the coast or navigable rivers, using the ‘Coastal access II’ measure – these areas are inflated in order to make them visible. Towns with coastal access are denoted by hexagons, and those that are not are denoted by squares. Colour figure can be viewed at wileyonlinelibrary.com. (3) is an indicator for the location of a town (in the Roman or later period); and are indicators for the earlier (typically Roman) and later (typically post‐Roman) periods, and is an indicator for coastal access at each point on our grid using either of our two measures, which are described above. We now proceed to test more formally whether Britain's towns had more coastal access in the Middle Ages than in the Roman era and whether or not this was the case for France. We begin by pooling a pair of cross‐sections of our grid, one using Roman era town locations, and the other using a later era's town locations. We then use these data to estimate regressions of the form:whereis an indicator for the location of a town (in the Roman or later period);andare indicators for the earlier (typically Roman) and later (typically post‐Roman) periods, andis an indicator for coastal access at each point on our grid using either of our two measures, which are described above. (4) We use these regressions to examine whether towns in Britain moved towards locations with coastal access from the Roman to later periods. Specifically, we test whether the ratio of the probability of finding a town in a location with coastal access to the probability of finding a town in a location without coastal access increased in Britain from the Roman to later periods. This ratio is useful, since it tells us by how much a particular locational fundamental (in this case coastal access) increased the odds of a town in a given location, in a given area and period. Formally, the test we conduct is as follows: (5) We also conduct an equivalent test for France: (6) Finally, we test whether the shift over time towards coastal access was more pronounced in Britain than in France: Table 3 shows that in Britain the effect of coastal access on towns (as reflected in the odds ratio discussed above) roughly tripled from the Roman era to the Middle Ages, and remained at its higher level at least until 1700. For the three cases where we observe a sizeable number of towns in Britain (towns measured in 1086–1200, 1377–1400, and in 1700) the increase is statistically significant, while for the remaining outcome (towns in 1200), where the number of towns we observe in Britain is smaller, the change is even larger in magnitude but only marginally significant. The Table also shows that French towns barely shifted towards locations with better coastal access. The magnitude of the ratios is also informative: in Britain in 1700 the ratio for the coastal access measures was around 6, implying that coastal access was as good a predictor of towns in 1700 as Roman towns (for which the ratio was around 7.5). In contrast, in France in 1700, the ratio for the coastal access measures was around 4, compared to the ratio for Roman towns which was almost 20. Finally, we note that the differential change between the two countries is typically either significant or marginally significant, again with more precision in cases where the number of towns in Britain is larger.50 Table 3. Location of Roman and Later Towns Dependent variable: Roman town (baseline) or later town Later town: Town with 1k+ people in 1086–1200 Town with 5k+ people in 1200 One of largest 50 towns in 1377–1400 Town with 5k+ people in 1700 Coastal access measure: I II I II I II I II Roman period 0.00023 0.00019 0.00023 0.00019 0.00023 0.00019 0.00023 0.00019 (0.00002) (0.00002) (0.00002) (0.00002) (0.00002) (0.00002) (0.00002) (0.00002) Roman period × Britain 0.00017 0.00019 0.00017 0.00019 0.00017 0.00019 0.00017 0.00019 (0.00008) (0.00008) (0.00008) (0.00008) (0.00008) (0.00008) (0.00008) (0.00008) Roman period × Coastal access 0.00071 0.00051 0.00071 0.00051 0.00071 0.00051 0.00071 0.00051 (0.00014) (0.00008) (0.00014) (0.00008) (0.00014) (0.00008) (0.00014) (0.00008) Roman period × Britain × Coastal access −0.00028 −0.00018 −0.00028 −0.00018 −0.00028 −0.00018 −0.00028 −0.00018 (0.00018) (0.00012) (0.00018) (0.00012) (0.00018) (0.00012) (0.00018) (0.00012) Later period 0.00011 0.00009 0.00008 0.00006 0.00006 0.00005 0.00022 0.00019 (0.00002) (0.00002) (0.00001) (0.00001) (0.00001) (0.00001) (0.00002) (0.00002) Later period × Britain 0.00003 0.00002 −0.00005 −0.00003 0.0001 0.00007 −0.00009 −0.00008 (0.00004) (0.00005) (0.00002) (0.00002) (0.00003) (0.00003) (0.00005) (0.00004) Later period × Coastal access 0.0004 0.0003 0.00031 0.00023 0.0003 0.0002 0.00082 0.00054 (0.00009) (0.00005) (0.00007) (0.00004) (0.00007) (0.00004) (0.00013) (0.00008) Later period × Britain × Coastal access 0.00033 0.00031 −0.00001 −0.00003 0.00041 0.00044 −0.00016 0.00001 (0.00016) (0.00011) (0.00011) (0.00007) (0.00014) (0.00011) (0.00018) (0.00012) Coastal access effects in Britain: on Roman towns (= C1) 2.08 1.87 2.08 1.87 2.08 1.87 2.08 1.87 on later towns (= C2) 6.09 6.3 12.18 7.49 5.41 6.64 5.89 6.36 Change in effect: C2/C1 − 1 1.93 2.37 4.86 3.01 1.6 2.55 1.83 2.4 Test H0: C2/C1 ≤ 1 versus H1: C2/C1 > 1, p‐value: 0.011 0.026 0.059 0.076 0.002 0.003 0.027 0.042 Coastal access effects in France: on Roman towns (= C3) 4.10 3.71 4.10 3.71 4.10 3.71 4.10 3.71 on later towns (= C4) 4.55 4.32 4.92 0.84 6.04 5.24 4.71 3.89 Change in effect: C4/C3 − 1 0.11 0.16 0.20 0.30 0.47 0.41 0.15 0.05 Test H0: C4/C3 ≤ 1 versus H1: C4/C3 > 1, p‐value: 0.333 0.263 0.236 0.102 0.0983 0.122 0.234 0.39 Differential change, Britain minus France: (C2/C1) − (C4/C3) 1.82 2.21 4.66 2.71 1.13 2.14 1.68 2.35 Test H0: (C2/C1) − (C4/C3) ≤ 0 versus H1:(C2/C1) − (C4/C3) > 0, p‐value: 0.029 0.029 0.059 0.088 0.072 0.009 0.07 0.057 Online Appendix Table A9 shows a similar comparison of Britain to northern France, instead of France as a whole. In northern France, the shift towards the coast is somewhat larger in magnitude than in France as a whole but, unlike in Britain, it is still not significant. Online Appendix Table A10 compares Britain to the whole of France but this time using only towns with defended areas of 5 hectares or more. While the sample is smaller and not all the estimates are precise, the picture that emerges is consistent with the results described above, with the urban network reconfiguring towards locations with coastal access in Britain but not in France. (7) is the population in town i in year t and the change in population is measured from 1200 until 1800 (a year for which we have population data for all towns with 5,000 people or more in 1200), or in alternative specifications until 1700 and 2012. 2007 We earlier noted that changes in transport technology meant that coastal access was probably more important for medieval towns than for Roman towns in Britain and France. But is there more direct evidence that coastal access actually mattered? While we have no causal evidence on the effect of coastal access on towns (since towns are a selected sample of points on our grid), we provide below evidence, which strongly suggests that it did. First, we use data on towns with 5,000 people or more in 1200 to estimate specifications of the type:whereis the population in townin yearand the change in population is measured from 1200 until 1800 (a year for which we have population data for all towns with 5,000 people or more in 1200), or in alternative specifications until 1700 and 2012. 51 As Table 4 shows, the population of towns with coastal access grew almost 10 percentage points faster per century from 1200 to 1800 than that of towns without coastal access. The estimates for growth from 1200 to 2012 are still sizeable but although smaller and less precise. This may be because since the Industrial Revolution the cost of building canals and maintaining them have fallen and the importance of coastal access decreased with the advent of trains and highways. If so, we are now again seeing an environment where road transport is a good substitute for land transport, and this particular advantage of coastal access has diminished. Other aspects of locational fundamentals, such as good weather, may now be more important, though (Rappaport,). But even if we are now back in an environment where maritime transport is not so important for most cities, our results suggest that having no coastal access was costly for towns’ growth prospects over more than half a millennium. Table 4. Coastal Access and the Growth of Towns with 5,000 People or More in 1200 Sample: Britain and France Britain and France Britain and France Britain and France Britain and France Britain and France, only areas ≤25 kilometres of coast or navigable river Britain and France, only Britannia, Belgica, and Lugdunensis North‐western Europe, all Roman provinces Britain and France Dependent variable is population growth from: 1200–1800 1200–1800 1200–1800 1200–1700 1200–2012 1200–1800 1200–1800 1200–1800 1200–1800 Panel (a): Coastal access measure I Coastal access 0.600 0.631 0.614 0.424 0.312 0.595 0.542 0.616 0.505 (0.177) (0.171) (0.170) (0.173) (0.224) (0.248) (0.282) (0.156) (0.185) ln(population in 1200) −0.202 −0.195 −0.108 −0.222 −0.179 −0.176 −0.251 −0.173 (0.140) (0.150) (0.157) (0.188) (0.196) (0.289) (0.120) (0.151) Britain 0.0618 0.145 0.629 0.105 0.176 0.0491 −0.467 (0.297) (0.289) (0.338) (0.373) (0.436) (0.287) (0.308) Coastal access × Britain 0.726 (0.484) Observations 77 77 77 72 74 50 41 119 77 Panel (b): Coastal access measure II Coastal access 0.551 0.611 0.577 0.424 0.349 0.642 0.67 0.538 0.464 (0.165) (0.153) (0.155) (0.159) (0.201) (0.189) (0.251) (0.138) (0.165) ln(population in 1200) −0.229 −0.209 −0.116 −0.232 −0.199 −0.124 −0.264 −0.183 (0.151) (0.158) (0.161) (0.191) (0.173) (0.273) (0.124) (0.158) Britain 0.195 0.236 0.687 0.247 0.313 0.156 −0.385 (0.293) (0.281) (0.320) (0.318) (0.389) (0.286) (0.311) Coastal access × Britain 0.765 (0.480) Observations 77 77 77 72 74 65 41 119 77 A second piece of evidence on the importance of coastal access for towns comes from the construction of canals. Thousands of kilometres of canals currently exist in both Britain and France, connecting many of their towns. These are the product of many centuries of costly construction and maintenance of canals, which itself strongly suggests the economic importance of access to waterways for towns. At least 40 of France's canals were begun from 1200 to 1800 and the total length today is over 1,880 kilometres (Dictionnaire des rivières et canaux de France 2013). We have no comparable list for Britain, but Blair (2007) discusses the importance of canals in medieval England. To examine the relation between access to canals and town growth for towns with poor (or no) coastal access (where Coastal Access I measure equals zero), we estimate regressions as in specification 7 using an indicator for canals instead of an indicator for coastal access. The results in online Appendix Table A11 suggest that faster growing towns with poor (or no) coastal access eventually received access to canals. While these results do not necessarily reflect the causal effect of canals, they are consistent with our argument that water transport was valuable for towns for many centuries. Given this evidence on the value of access to water transportation routes, it is therefore striking that so many medieval French towns had no coastal access. Our finding that the French urban network did not realign towards locations with natural coastal access suggests that the path dependence in their location was in fact consequential. Still, even if coastal access was important, is it possible that there were no plausible locations with coastal access near medieval French towns? To examine this possibility, we define a location as ‘locally suboptimal’ if it is further than 5 kilometres, but no further than 25 kilometres, from a coast or a navigable river. The idea is that for towns in these suboptimal locations there is a plausible site nearby on which the town may have been built with better coastal access. We use a specification similar to 3, replacing the indicator for coastal access with an indicator for ‘local suboptimality’. We then test whether towns in Britain moved significantly away from locally suboptimal locations; whether the same can be said of France; and whether the movement away from suboptimal locations was similar in Britain and France. The results in online Appendix Table A12 show that towns in Britain moved away from locally suboptimal locations between the Roman era and the medieval era. At the same time, there was almost no movement away from locally suboptimal locations in France. Finally, the Table shows that the difference in changes between the two countries is large and statistically significant. It is difficult to ascertain how much faster the French urban network would have grown from 1200 to 1800 if its towns all had coastal access. Our estimates from Table 4 suggest that coastal access was associated with roughly 50% more population growth over the period. Aggregating this up to the network level requires strong assumptions about the complementarity or substitutability of different towns’ growth. But it is nevertheless plausible that the lack of coastal access of many French towns had a significant aggregate impact. But if Roman‐era locations imposed high costs for French towns, we might wonder why their population did not relocate during the early Middle Ages, when towns were relatively small and weak. In online Appendix C, we discuss one possible explanation, which emphasises the role of bishops. As Nicholas (1997) and Wickham (2009) discuss, bishops and their followers played important roles in town life in France after the fall of the Western Roman Empire. In the online Appendix, we show that Roman towns in France, which were bishoprics (home to bishops) in the fourth century, before the Roman Empire's collapse, were more likely than others to survive through the Middle Ages and up to the present day. Interestingly, Roman‐era towns without bishops in France were about as (un)likely to survive as Roman towns in Britain.52 We conclude by noting that even if religious considerations made bishopric locations viable in France, any locational advantage that they conferred was the result of people's investments.53 In other words, French towns stayed in locations with poor first‐nature fundamentals because they were home to concentrations of people and because of the value of physical and cultural investments made in those locations. Today, many cities around the world concentrate many more people than in the past and much more physical and cultural capital. Our findings suggest that this could allow them to remain stranded in locations that are even more unsuitable in terms of their physical geography.

4 Conclusions The collapse of the Roman Empire temporarily ended urbanisation in Britain but not in France. We find that as urbanisation recovered in the Middle Ages, the location of towns in France was closely related to their Roman predecessors. This was not, however, the case in Britain, whose urban network largely realigned. We find that Britain's medieval towns benefited from better coastal access than their French counterparts. We also find that from the Middle Ages until the Industrial Revolution, towns with coastal access grew more quickly than others, in both Britain and France. Our estimates suggest that with better coastal access, France's urban population would have been considerably larger in 1800. Taken together, our findings suggest that France's towns remained trapped in locations without coastal access. We interpret this as evidence for consequential path dependence in the location of economic activity. In other words, once economic activity concentrates in a given location, it can persist there for many centuries even if the location is no longer optimal. Today's major cities are much larger than their historical counterparts and may therefore be even more persistent if their locations become ill‐suited. Our evidence is important in an increasingly urbanised world. While in the developed world coastal access may no longer be as important as it once was, it may still relevant for parts of the developing world, where trade costs are high. And even in the developed world, many large urban centres are located in areas susceptible to natural disasters, such as earthquakes and flooding. Our paper's findings underscore the importance of decisions on the location of urban infrastructure. Policies that affect the location of cities may have important consequences for generations to come.

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