During the last four decades the Crusades have become one of the most dynamic areas of historical enquiry, which points to an increasing curiosity to understand and interpret these extraordinary events. What persuaded people in the Christian West to want to recapture Jerusalem? What impact did the success of the First Crusade (1099) have on the Muslim, Christian and Jewish communities of the eastern Mediterranean? What was the effect of crusading on the people and institutions of western Europe? How did people record the Crusades and, finally, what is their legacy?

Academic debate moved forwards significantly during the 1980s, as discussion concerning the definition of a crusade gathered real steam. Understanding of the scope of the Crusades widened with a new recognition that crusading extended far beyond the original 11th-century expeditions to the Holy Land, both in terms of chronology and scope. That is, they took place long after the end of the Frankish hold on the East (1291) and continued down to the 16th century. With regards to their target, crusades were also called against the Muslims of the Iberian peninsula, the pagan peoples of the Baltic region, the Mongols, political opponents of the Papacy and heretics (such as the Cathars or the Hussites). An acceptance of this framework, as well as the centrality of papal authorisation for such expeditions, is generally referred to as the 'pluralist' position.

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The emergence of this interpretation energised the existing field and had the effect of drawing in a far greater number of scholars. Alongside this came a growing interest in re-evaluating the motives of crusaders, with some of the existing emphases on money being downplayed and the cliché of landless younger sons out for adventure being laid to rest. Through the use of a broader range of evidence than ever before (especially charters, that is sales or loans of lands and/or rights), a stress on contemporary religious impulses as the dominant driver for, particularly the First Crusade, came through. Yet the wider world intruded on and then, in some ways, stimulated this academic debate: the horrors of 9/11 and President George W. Bush's disastrous use of the word 'crusade' to describe the 'war on terror' fed the extremists' message of hate and the notion of a longer, wider conflict between Islam and the West, dating back to the medieval period, became extremely prominent. In reality, of course, such a simplistic view is deeply flawed but it is a powerful shorthand for extremists of all persuasions (from Osama Bin Laden to Anders Breivik to ISIS) and certainly provided an impetus to study the legacy of the crusading age into the modern world, as we will see here, calling on the extensive online archive of History Today.

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The First Crusade was called in November 1095 by Pope Urban II at the town of Clermont in central France. The pope made a proposal: 'Whoever for devotion alone, but not to gain honour or money, goes to Jerusalem to liberate the Church of God can substitute this journey for all penance.' This appeal was the combination of a number of contemporary trends along with the inspiration of Urban himself, who added particular innovations to the mix. For several decades Christians had been pushing back at Muslim lands on the edge of Europe, in the Iberian peninsula, for example, as well as in Sicily. In some instances the Church had become involved in these events through the offer of limited spiritual rewards for participants.

Urban was responsible for the spiritual well-being of his flock and the crusade presented an opportunity for the sinful knights of western Europe to cease their endless in-fighting and exploitation of the weak (lay people and churchmen alike) and to make good their violent lives. Urban saw the campaign as a chance for knights to direct their energies towards what was seen as a spiritually meritorious act, namely the recovery of the holy city of Jerusalem from Islam (the Muslims had taken Jerusalem in 637). In return for this they would, in effect, be forgiven those sins they had confessed. This, in turn, would save them from the prospect of eternal damnation in the fires of Hell, a fate repeatedly emphasised by the Church as the consequence of a sinful life. To find out more see Marcus Bull, who reveals the religious context of the campaign in his 1997 article.

Within an age of such intense religiosity the city of Jerusalem, as the place where Christ lived, walked and died, held a central role. When the aim of liberating Jerusalem was coupled to lurid (probably exaggerated) stories of the maltreatment of both the Levant's native Christians and western pilgrims, the desire for vengeance, along with the opportunity for spiritual advancement, formed a hugely potent combination. Urban would be looking after his flock and improving the spiritual condition of western Europe, too. The fact that the papacy was engaged in a mighty struggle with the German emperor, Henry IV (the Investiture Controversy), and that calling the crusade would enhance the pope's standing was an opportunity too good for Urban to miss.

A spark to this dry tinder came from another Christian force: the Byzantine Empire. Emperor Alexios I feared the advance of the Seljuk Turks towards his capital city of Constantinople. The Byzantines were Greek Orthodox Christians but, since 1054, had been in a state of schism with the Catholic Church. The launch of the crusade presented Urban with a chance to move closer to the Orthodox and to heal the rift.

The reaction to Urban's appeal was astounding and news of the expedition rippled across much of the Latin West. Thousands saw this as a new way to attain salvation and to avoid the consequences of their sinful lives. Yet aspirations of honour, adventure, financial gain and, for a very small number, land (in the event, most of the First Crusaders returned home after the expedition ended) may well have figured, too. While churchmen frowned upon worldly motives because they believed that such sinful aims would incur God's displeasure, many laymen had little difficulty in accommodating these alongside their religiosity. Thus Stephen of Blois, one of the senior men on the campaign, could write home to his wife, Adela of Blois (daughter of William the Conqueror), that he had been given valuable gifts and honours by the emperor and that he now had twice as much gold, silver and other riches as when he left the West. People of all social ranks (except kings) joined the First Crusade, although an initial rush of ill-disciplined zealots sparked an horrific outbreak of antisemitism, especially in the Rhineland, as they sought to finance their expedition by taking Jewish money and to attack a group perceived as the enemies of Christ in their own lands. These contingents, known as the 'Peoples' Crusade', caused real problems outside Constantinople, before Alexios ushered them over the Bosporus and into Asia Minor, where the Seljuk Turks destroyed them.

Led by a series of senior nobles, the main armies gathered in Constantinople during 1096. Alexios had not expected such a huge number of westerners to appear on his doorstep but saw the chance to recover land lost to the Turks. Given the crusaders' need for food and transport, the emperor held the upper hand in this relationship, although this is not to say that he was anything other than cautious in dealing with the new arrivals, particularly in the aftermath of the trouble caused by the Peoples' Crusade and the fact that the main armies included a large Norman Sicilian contingent, a group who had invaded Byzantine lands as recently as 1081. See Peter Frankopan. Most of the crusade leaders swore oaths to Alexios, promising to hand over to him lands formerly held by the Byzantines in return for supplies, guides and luxury gifts.

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In June 1097 the crusaders and the Greeks took one of the emperor's key objectives, the formidable walled city of Nicaea, 120 miles from Constantinople, although in the aftermath of the victory some writers reported Frankish discontent at the division of booty. The crusaders moved inland, heading across the Anatolian plain. A large Turkish army attacked the troops of Bohemond of Taranto near Dorylaeum. The crusaders were marching in separate contingents and this, plus the unfamiliar tactics of swift attacks by mounted horse archers, almost saw them defeated until the arrival of forces under Raymond of Toulouse and Godfrey of Bouillon saved the day. This hard-won victory proved an invaluable lesson for the Christians and, as the expedition went on, the military cohesion of the crusader army grew and grew, making them an ever more effective force.

Over the next few months the army, under Count Baldwin of Boulogne, crossed Asia Minor with some contingents taking the Cilician towns of Tarsus and Mamistra and others, heading via Cappadocia towards the eastern Christian lands of Edessa (biblical Rohais), where the largely Armenian population welcomed the crusaders. Local political conflict meant Baldwin was able to take power himself and thus, in 1098, the first so-called Crusader State, the County of Edessa, came into being.

By this time the bulk of the army had reached Antioch, today just inside the southern Turkish border with Syria. This huge city had been a Roman settlement; to Christians it was significant as the place where saints Peter and Paul had lived and it was one of the five patriarchal seats of the Christian Church. It was also important to the Byzantines, having been a major city in their empire as recently as 1084. The site was too big to surround properly but the crusaders did their best to squeeze the place into submission. Over the winter of 1097 conditions became extremely harsh, although the arrival of a Genoese fleet in the spring of 1098 provided some useful support. The stalemate was only ended when Bohemond persuaded a local Christian to betray one of the towers and on June 3rd, 1098 the crusaders broke into the city and captured it. Their victory was not complete, however, because the citadel, towering over the site, remained in Muslim hands, a problem compounded by the news that a large Muslim relief army was approaching from Mosul. Lack of food and the loss of most of their horses (essential for the knights, of course) meant that morale was at rock bottom. Count Stephen of Blois, one of the most senior figures on the crusade, along with a few other men, had recently deserted, believing the expedition doomed. They met Emperor Alexios, who was bringing long-awaited reinforcements, and told him that the crusade was a hopeless cause. Thus, in good faith, the Greek ruler turned back. In Antioch, meanwhile, the crusaders had been inspired by the 'discovery' of a relic of the Holy Lance, the spear that had pierced Christ's side as he was on the cross. A vision told a cleric in Raymond of St Gilles' army where to dig and, sure enough, there the object was found. Some regarded this as a touch convenient and too easy a boost to the standing of the Provençal contingent, but to the masses it acted as a vital inspiration. A couple of weeks later, on June 28th, 1098, the crusaders gathered their last few hundred horses together, drew themselves into their now familiar battle lines and charged the Muslim forces. With writers reporting the aid of warrior saints in the sky, the crusaders triumphed and the citadel duly surrendered leaving them in full control of Antioch before the Muslim relief army arrived.

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In the aftermath of victory many of the exhausted Christians succumbed to disease, including Adhémar of Le Puy, the papal legate and spiritual leader of the campaign. The senior crusaders were bitterly divided. Bohemond wanted to stay and consolidate his hold on Antioch, arguing that since Alexios had not fulfilled his side of the bargain then his oath to the Greeks was void and the conquest remained his. The bulk of the crusaders scorned this political squabbling because they wanted to reach Christ's tomb in Jerusalem and they compelled the army to head southwards. En route, they avoided major set-piece confrontations by making deals with individual towns and cities and they reached Jerusalem in June 1099. John France relates the capture of the city in his article from 1997.

Forces concentrated to the north and the south of the walled city and on July 15th, 1099 the troops of Godfrey of Bouillon managed to bring their siege towers close enough to the walls to get across. Their fellow Christians burst into the city and over the next few days the place was put to the sword in an outburst of religious cleansing and a release of tension after years on the march. A terrible massacre saw many of the Muslim and Jewish defenders of the city slaughtered, although the oft-repeated phrase of 'wading up to their knees in blood' is an exaggeration, being a line from the apocalyptic Book of Revelation (14:20) used to convey an impression of the scene rather than a real description – a physical impossibility. The crusaders gave emotional thanks for their success as they reached their goal, the tomb of Christ in the Holy Sepulchre.

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Their victory was not yet assured. The vizier of Egypt had viewed the crusaders' advance with a mixture of emotions. As the guardian of the Shi'ite caliphate in Cairo he had a profound dislike of the Sunni Muslims of Syria, but equally he did not want a new power to establish itself in the region. His forces confronted the crusaders near Ascalon in August 1099 and, in spite of their numerical inferiority, the Christians triumphed and also secured a substantial amount of booty. By this time, having achieved their aims, the vast majority of the exhausted crusaders were only too keen to return to their homes and families. Some, of course, chose to remain in the Levant, resolved to guard Christ's patrimony and to set up lordships and holdings for themselves. Fulcher of Chartres, a contemporary in the Levant, lamented that only 300 knights stayed in the kingdom of Jerusalem; a tiny number to establish a permanent hold on the land.

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Over the next decade, however, aided by the lack of real opposition from the local Muslims and boosted by the arrival of a series of fleets from the West, the Christians began to take control of the whole coastline and to create a series of viable states. The support of the Italian trading cities of Venice, Pisa and, particularly at this early stage, Genoa, was crucial. The motives of the Italians have often been questioned but there is convincing evidence to show they were just as keen as any other contemporaries to capture Jerusalem, yet as trading centres they were determined to advance the cause of their home city, too. The writings of Caffaro of Genoa, a rare secular source from this period, show little difficulty in assimilating these motives. He went on pilgrimage to the River Jordan, attended Easter ceremonies in the Holy Sepulchre and celebrated the acquisition of riches. Italian sailors and troops helped capture the vital coastal ports (such as Acre, Caesarea and Jaffa), in return for which they were awarded generous trading privileges which, in turn, gave a vital boost to the economy as the Italians transported goods from the Muslim interior (especially spices) back to the West. Just as important was their role in bringing pilgrims to and from the Holy Land. Now that the holy places were in Christian hands, many thousands of westerners could visit the sites and, as they came under Latin control, religious communities flourished. Thus, the basic rationale behind the Crusades was fulfilled. There is a strong case for saying that the crusader states could not have been sustained were it not for the contribution of the Italians.

One interesting side-effect of the First Crusade (and a matter of immense interest to scholars today) is the unprecedented burst of historical writing that emerged after the capture of Jerusalem. This amazing episode inspired authors across the Christian West to write about these events in a way that nothing in earlier medieval history had done. No longer had they to look back to the heroes of antiquity, because their own generation had provided men of comparable renown. This was an age of rising literacy and the creation and circulation of crusade texts was a big part of this movement. Numerous histories, plus oral storytelling, often in the form of Chansons de geste, popular within the early flowerings of the chivalric age, celebrated the First Crusade. Historians have previously looked at these narratives to construct the framework of events but now many scholars are looking behind these texts to consider more deeply the reasons why they were written, the different styles of writing, the use of classical and biblical motifs, the inter-relationships and the borrowings between the texts.

Another area to receive increasing attention is the reaction of the Muslim world. It is now clear that when the First Crusade arrived the Muslims of the Near East were extremely divided, not just along the Sunni/Shi'ite fault line, but also, in the case of the former, among themselves. Robert Irwin draws attention to this in his 1997 article, as well as considering the impact of the crusade on the Muslims of the region. It was a fortunate coincidence that during the mid-1090s the death of senior leaders in the Seljuk world meant that the crusaders encountered opponents who were primarily concerned with their own political infighting rather than seeing the threat from outside. Given that the First Crusade was, self-evidently, a novel event, this was understandable. The lack of jihad spirit was also evident, as lamented by as-Sulami, a Damascene preacher whose urging of the ruling classes to pull themselves together and fulfil their religious duty was largely ignored until the time of Nur ad-Din (1146-74) and Saladin onwards.

The Frankish settlers had to fit in to the complex cultural and religious blend of the Near East. Their numbers were so few that once they had captured places they very quickly needed to adapt their behaviour from the militant holy war rhetoric of Pope Urban II to a more pragmatic stance of relative religious toleration, with truces and even occasional alliances with various Muslim neighbours. Had they oppressed the majority local population (and many Muslims and eastern Christians lived under Frankish rule), there would have been no-one to farm the lands or to tax and their economy would simply have collapsed. Recent archaeological work by the Israeli scholar Ronnie Ellenblum has done much to show that the Franks did not, as was previously believed, live solely in the cities, separated from the local populace. Local Christian communities often existed alongside them, sometimes even sharing churches.

The Frankish states of Edessa, Antioch, Tripoli and Jerusalem established themselves in the complex religious, political and cultural landscape of the Near East. One of the early rulers of Jerusalem had married into native Armenian Christian nobility and thus Queen Melisende (1131-52) had a strong interest in supporting the indigenous as well as the Latin Church. The quirks of genetics, coupled with a high mortality rate among male rulers, meant that women exerted greater power than previously supposed given the war-torn environment of the Latin East and prevailing religious attitudes towards women as weak temptresses. It still needed a strong personality to survive and, in the case of Melisende, that was certainly so, as Simon Sebag Montefiore recounts in a 2011 article, which also gives a sense of the city of Jerusalem during the 12th century, as well as some contemporary Muslim views of the Christian settlers.

The Franks were always short on manpower but were a dynamic group who developed innovative institutions, such as the Military Orders, to survive. The Orders were founded to help look after pilgrims; in the case of the Hospitallers, through healthcare; in that of the Templars, to guard visitors on the road to the River Jordan. Soon both were fully-fledged religious institutions, whose members took the monastic vows of poverty, chastity and obedience. It proved a popular concept and donations from admiring and grateful pilgrims meant that the Military Orders developed a major role as landowners, as the custodians of castles and as the first real standing army in Christendom. They were independent of the control of the local rulers and could, at times, cause trouble for the king or squabble with one another. The Templars and Hospitallers also held huge tracts of land across western Europe, which provided income for the fighting machine in the Levant, especially the construction of the castles that became so vital to the Christian hold on the region.

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In December 1144 Zengi, the Muslim ruler of Aleppo and Mosul, captured Edessa to mark the first major territorial setback for the Franks of the Near East. The news of this disaster prompted Pope Eugenius III to issue an appeal for the Second Crusade (1145-49). Fortified by this powerful call to live up to the deeds of their first crusading forefathers, coupled with the inspiring rhetoric of (Saint) Bernard of Clairvaux, the rulers of France and Germany took the cross to mark the start of royal involvement in the Crusades. Christian rulers in Iberia joined with the Genoese in attacking the towns of Almeria in southern Spain (1147) and Tortosa in the north-east (1148); likewise the nobles of northern Germany and the rulers of Denmark launched an expedition against the pagan Wends of the Baltic shore around Stettin. While this was no grand plan of Pope Eugenius but rather a reaction to appeals sent to him, it shows the confidence in crusading at this time. In the event, this optimism proved deeply unfounded. A group of Anglo-Norman, Flemish and Rhineland crusaders captured Lisbon in 1147 and the other Iberian campaigns were also successful but the Baltic campaign achieved virtually nothing and the most prestigious expedition of all, that to the Holy Land, was a disaster, as Jonathan Phillips explains in his 2007 article. The two armies lacked discipline, supplies and finance, and both were badly mauled by the Seljuk Turks as they crossed Asia Minor. Then, in conjunction with the Latin settlers, the crusaders laid siege to the most important Muslim city in Syria, Damascus. Yet, after only four days, fear of relief forces led by Zengi's son, Nur ad-Din, prompted an ignominious retreat. The crusaders blamed the Franks of the Near East for this failure, accusing them of accepting a pay-off to retreat. Whatever the truth in this, the defeat at Damascus certainly damaged crusade enthusiasm in the West and over the next three decades, in spite of increasingly elaborate and frantic appeals for help, there was no major crusade to the Holy Land.

To regard the Franks as entirely enfeebled would, however, be a serious error. They captured Ascalon in 1153 to complete their control of the Levantine coast, an important advance for the security of trade and pilgrim traffic in terms of reducing harassment by Muslim shipping. The following year, however, Nur ad-Din took power in Damascus to mark the first time that the cities had been joined with Aleppo under the rule of the same man during the crusader period, something that greatly increased the threat to the Franks. Nur ad-Din's considerable personal piety, his encouragement of madrasas (teaching colleges) and the composition of jihad poetry and texts extolling the virtues of Jerusalem created a bond between the religious and the ruling classes that had been conspicuously lacking since the crusaders arrived in the East. During the 1160s Nur ad-Din, acting as the champion of Sunni orthodoxy, seized control of Shi'ite Egypt, dramatically raising the strategic pressure on the Franks and at the same time enhancing the financial resources at his disposal through the fertility of the Nile Delta and the vital port of Alexandria.

This period of the history of the Latin East is related in detail by the most important historian of the age, William, Archbishop of Tyre, as Peter Edbury describes. William was an immensely educated man, who soon became embroiled in the bitter political struggles of the late 1170s and 1180s during the reign of the tragic figure of King Baldwin IV (1174-85), a youth afflicted by leprosy. The need to establish his successor provided an opportunity for rival factions to emerge and to cause the Franks to expend much of their energy on bickering with each other. That is not to say that they were unable to inflict serious damage on Nur ad-Din's ambitious successor, Saladin, who from his base in Egypt, hoped to usurp his former master's dynasty, draw the Muslim Near East together and to expel the Franks from Jerusalem. Norman Housely expertly relates this period in his 1987 article. In 1177, however, the Franks triumphed at the Battle of Montgisard, a victory that was widely reported in western Europe and did little to convince people of the settlers' very real need for help. The construction in 1178 and 1179 of the large castle of Jacob's Ford, only a day's ride from Damascus, was another aggressive gesture that required Saladin to destroy the place. Yet by 1187 the sultan had gathered a large, but fragile coalition of warriors from Egypt, Syria and Iraq that was sufficient to bring the Franks into the field and to inflict upon them a terrible defeat at Hattin on July 4th. Within months, Jerusalem fell and Saladin had recovered Islam's third most important city after Mecca and Medina, an achievement that still echoes down the centuries.

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News of the calamitous fall of Jerusalem sparked grief and outrage in the West. Pope Urban III was said to have died of a heart attack at the news and his successor, Gregory VIII, issued an emotive crusade appeal and the rulers of Europe began to organise their forces. Frederick Barbarossa's German army successfully defeated the Seljuk Turks in Asia Minor only for the emperor to drown crossing a river in southern Turkey. Soon afterwards many of the Germans died of sickness and Saladin escaped facing this formidable enemy. The Franks in the Levant had managed to cling onto the city of Tyre and then besieged the most important port on the coast, Acre. This provided a target for western forces and it was here in the summer of 1190 that Philip Augustus and Richard the Lionheart landed. The siege had lasted almost two years and the arrival of the two western kings and their troops gave the Christians the momentum they needed. The city surrendered and Saladin's prestige was badly dented. Philip soon returned home and while Richard made two attempts to march on Jerusalem, fears as to its long-term prospects after he left meant that the holy city remained in Muslim hands. Thus the Third Crusade failed in its ultimate objective, although it did at least allow the Franks to recover a strip of lands along the coast to provide a springboard for future expeditions. For his part, Saladin had suffered a series of military setbacks but, crucially, he had held onto Jerusalem for Islam.

The pontificate of Innocent III (1198-1216) saw another phase in the expansion of crusading. Campaigns in the Baltic advanced further and the holy war in Iberia stepped forwards too. In 1195 Muslims had crushed Christian forces at the Battle of Alarcos, which, so soon after the disaster at Hattin, seemed to show God's deep displeasure with his people. By 1212, however, the rulers of Iberia managed to pull together to rout the Muslims at the Battle of Las Navas de Tolosa to seal a major step in the recovery of the peninsula. That said, the particular cultural, political and religious make-up of the region mean that it would be wrong, as in the Holy Land, to characterise relations between religious groups as constant warfare, a situation outlined by Robert Burns and Paul Chevedden. In southern France, meanwhile, efforts to curb the Cathar heresy had failed and, in a bid to defeat this sinister threat to the Church in its own backyard, Innocent authorised a crusade to the area. See the piece by Richard Cavendish. Catharism was a dualist faith, albeit with a few links to mainstream Christian practice, but it also had its own hierarchy and was intent upon replacing the existing elite. Years of warfare ensued as the crusaders, led by Simon de Monfort, sought to drive the Cathars out, but ultimately their roots in southern French society meant they could endure and it was only the more pervasive techniques of the Inquisition, initiated in the 1240s, that succeeded where force had failed.

The most infamous episode of the age was the Fourth Crusade (1202-04) which saw another effort to recover Jerusalem end up sacking Constantinople, the greatest Christian city in the world. Jonathan Phillips describes this episode. The reasons for this were a combination of long-standing tensions between the Latin (Catholic) Church and the Greek Orthodox; the need for the crusaders to fulfil the terms of a wildly over-optimistic contract for transportation to the Levant with the Venetians and the offer to pay this off by a claimant to the Byzantine throne. This combination of circumstances brought the crusaders to the walls of Constantinople and when their young candidate was murdered and the locals turned definitively against them they attacked and stormed the city. At first Innocent was delighted that Constantinople was under Latin authority but as he learned of the violence and looting that had accompanied the conquest he was horrified and castigated the crusaders for 'the perversion of their pilgrimage'.

One consequence of 1204 was the creation of a series of Frankish States in Greece that, over time, also needed support. Thus, in the course of the 13th century, crusades were preached against these Christians, although by 1261 Constantinople itself was back in Greek hands.

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In spite of this series of disasters, it is interesting to see that crusading remained an attractive concept, something made manifest by the near-legendary Children's Crusade of 1212. Inspired by divine visions, two groups of young peasants (best described as youths, rather than children) gathered around Cologne and near Chartres in the belief that their purity would ensure divine approval and enable them to recover the Holy Land. The German group crossed the Alps and some reached the port of Genoa, where the harsh realities of having no money or real hope of achieving anything was made plain when they were refused passage to the East and the entire enterprise collapsed.

Thus, the early 13th century was characterised by the diversity of crusading. Holy war was proving a flexible and adaptable concept that allowed the Church to direct force against its enemies on many fronts. The rationale of crusading, as a defensive act to protect Christians, could be refined to apply specifically to the Catholic Church and thus when the papacy came into conflict with Emperor Frederick II over the control of southern Italy it eventually called a crusade against him. Frederick had already been excommunicated for failing to fulfil his promises to take part in the Fifth Crusade. This expedition had achieved the original intention of the Fourth Crusade by invading Egypt but became bogged down outside the port of Damietta before a poorly executed attempt to march on Cairo collapsed. Frederick's attempts to make good this were frustrated by genuine ill health but by this time the papacy had lost patience with him. Recovered, Frederick went to the Holy Land as, by this time, king of Jerusalem (by marriage to the heiress to the throne) where – irony of ironies – as an excommunicate, he negotiated the peaceful restoration of Jerusalem to the Christians. His diplomatic skills (he spoke Arabic), the danger posed by his considerable resources as well as the divisions in the Muslim world in the decades after Saladin's death, enabled him to accomplish this. A brief period of better relations between pope and emperor followed, but by 1245 the curia described him as a heretic and authorised the preaching of a crusade against him.

Aside from the plethora of crusading expeditions that took place over the centuries, we should also remember that the launch of such campaigns had a profound impact on the lands and people from whence they came, something covered by Christopher Tyerman. Crusading required substantial levels of financial support and this, over time, saw the emergence of national taxes to support such efforts, as well as efforts to raise money from within the Church itself. The absence of a large number of senior nobles and churchmen could affect the political balance of an area, with opportunities for women to act as regents or for unscrupulous neighbours to defy ecclesiastical legislation and to try to take the lands of absent crusaders. The death or disappearance of a crusader, be they a minor figure or an emperor, obviously carried deep personal tragedy for those they had left behind, but might also precipitate instability and change.

The previous year, Jerusalem had fallen back into Muslim hands and this was the principal prompt for what turned out to be the greatest crusade expedition of the century (known as the Seventh Crusade) led by King (later Saint) Louis IX of France. Simon Lloyd outlines Louis's crusading career. Well financed and carefully prepared and with an early victory at Damietta, this campaign appeared to be set fair only for a reckless charge by Louis's brother at the Battle of Mansourah to weaken the crusaders' forces. This, coupled with hardening Muslim resistance, brought the expedition to a halt and, starving and sick, they were forced to surrender. Louis remained in the Holy Land for a further four years – a sign of his guilt at the failure of the campaign, but also a remarkable commitment for a European monarch to be absent from his home for a total of six years – trying to bolster the defences of the Latin kingdom. By this time, with the Latins largely confined to the coastal strip the settlers relied more and more on massive fortifications and it was during the 13th century that mighty castles such as Krak des Chevaliers, Saphet and Chastel Pelerin, as well as the immense urban fortifications of Acre, took shape.

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By this stage the political complexion of the Middle East was changing. The Mongol invaders added another dimension to the struggle as they conquered much of the Muslim world to the East; they had also briefly threatened Eastern Europe with savage incursions in 1240-41 (which also prompted a crusade appeal). Saladin's successors were displaced by the Mamluks, the former slave-soldiers, whose figurehead, the sultan Baibars, was a ferocious exponent of holy war and did much to bring the crusader states to their knees over the next two decades. James Waterson describes their advance. Bouts of in-fighting among the Frankish nobility, further complicated by the involvement of the Italian trading cities and the Military Orders served to further weaken the Latin States and finally, in 1291, the Sultan al-Ashraf smashed into the city of Acre to end the Christian hold on the Holy Land.

Some historians used to regard this as the end of the crusades but, as noted above, since the 1980s there has been a broad recognition that this was not the case, not least because of the series of plans made to try to recover the Holy Land during the 14th century. Elsewhere crusading was still a powerful idea, not least in northern Europe, where the Teutonic Knights (originally founded in the Holy Land) had transferred their interests and where they had created what was effectively an autonomous state. By the early 15th century, however, their enemies in the region were starting to Christianise anyway and thus it became impossible to justify continued conflict in terms of holy war. The success of Las Navas de Tolosa had effectively pinned the Muslims down to the very south of the Iberian peninsula, but it took until 1492 when Ferdinand and Isabella brought the full strength of the Spanish crown to bear upon Granada that the reconquest was completed. Plans to recover the Holy Land had not entirely died out and in a spirit of religious devotion, Christopher Columbus set out the same year hoping to find a route to the Indies that would enable him to reach Jerusalem from the East.

The 14th century began with high drama: the arrest and imprisonment of the Knights Templar on charges of heresy, a story related by Helen Nicholson. A combination of lax religious observance and their failure to protect the Holy Land had made them vulnerable. This uncomfortable situation, coupled with the French crown owing them huge sums of money (the Templars had emerged as a powerful banking institution) meant that the manipulative and relentless Philip IV of France could pressure Pope Clement V into suppressing the Order in 1312 and one of the great institutions of the medieval age was terminated.

Crusading within Europe itself had continued to mutate, too. The papacy had issued crusading indulgences on many occasions during its own struggles against both political enemies and against heretical groups such as the Hussites of Bohemia. The main threat to Christendom by this time, however, was from the Ottoman Turks, who, as Judith Herrin relates, captured Constantinople in 1453. Numerous efforts were made to draw together the leaders of the Latin West, but the growing power of nation states and their increasingly engrained conflicts, exemplified by the Hundred Years' War, meant that there was little appetite for the kind of Europe-wide response that had been seen in 1187, for example. Nigel Saul outlines this period of crusading history in his article.

Certain dynasties such as the dukes of Burgundy, were enthusiastic about the idea of crusading and a couple of reasonably-sized expeditions took place, although the Burgundians and the Hungarians were thrashed at Nicopolis in Bulgaria in 1396. By the middle of the 15th century the Ottomans had already twice besieged Constantinople and in 1453 Sultan Mehmet II brought forwards an immense army to achieve his aim. Last-minute appeals to the West brought insufficient help and the city fell in May. The Emperor Charles V invoked the crusading spirit in his defence of Vienna in 1529, although this struggle resembled more of an imperial fight rather than a holy war. Crusading had almost run its course; people had become increasingly cynical about the Church's sale of indulgences. The advance of the Reformation was another obvious blow to the idea, with crusading being viewed as a manipulative and money-making device of the Catholic Church. By the late 16th century the last real vestiges of the movement could be seen; the Spanish Armada of 1588 benefitted from crusade indulgences, while the Knights Hospitaller, who had first ruled Rhodes from 1306 to 1522 before making their base on Malta, inspired a remarkable victory over an Ottoman fleet at the Battle of Lepanto in 1571. Jonathan Riley-Smith relates the knights' story. The Hospitallers of Malta had also survived a huge Turkish siege in 1480 and their existence served as a long-lasting relic of the original crusading conflict until Napoleon Bonaparte extinguished their rule of the island in 1798.

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Crusading survived in the memory and the imagination of the peoples of western Europe and the Middle East. In the former, it regained profile through the romantic literature of writers such as Sir Walter Scott and, as lands in the Middle East fell to the imperialist empires of the age, the French, in particular, chose to draw links with their crusading past. The word became a shorthand for a cause with moral right, be it in a non-military context, such as a crusade against drink, or in the horrors of the First World War. General Franco's ties with the Catholic Church in Spain invoked crusading ideology in perhaps the closest modern incarnation of the idea and it remains a word in common usage today.

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In the Muslim world, the memory of the Crusades faded, although did not disappear, from view and Saladin continued to be a figure held out as an exemplar of a great ruler. In the context of the 19th century, the Europeans' invocation of the past built upon this existing memory and meant that the image of hostile, aggressive westerners seeking to conquer Muslim or Arab lands became extremely potent for Islamists and Arab Nationalist leaders alike, and Saladin, as the man who recaptured Jerusalem, stands as the man to aspire to. Articles by Jonathan Phillips and Umej Bhatia cover the memory and the legacy of the crusades to bring the story down to modern times.

Jonathan Phillips is Professor of Crusading History at Royal Holloway University of London and the author of Holy Warriors: A Modern History of the Crusades (Vintage, 2010).