In the course of the ninth century, Carolingian rulers developed a military infrastructure aimed at supporting expeditions to ensure Frankish control of the central Danubian watergate, the confluences of the Drava, Sava, Drina, Tisza, and southern Morava rivers with the Danube. Itineraries suggest that many Carolingian campaigns against Moravia were launched from royal palaces in upper Bavaria, not from localities along the Danube. As for expeditions that did proceed along the Danube, those forces marched southeast from Vienna toward Baden and Pitten in the direction of Ptuj or via Sopron toward Szombathely and, then, on to Lake Balaton and Pécs. Military operations against the Moravians were often accompanied by grants to royal supporters involving land along routes leading southeast, the very routes that armies marching toward the Danubian watergate would have taken. Finally, it can be shown that Carantania became the most important lordship in this Frankish marcher organization. Prosopographical research demonstrates that almost all of the major figures in the marches were closely connected with Carantania. The preeminence of Carantania in the military system of the Carolingian marches is difficult to comprehend, if Moravian centers were located in the modern Czech Republic.

Traditional military histories of the Middle Ages conclude that there was very little “art” involved in early medieval war. Though battles were sometimes bloody brawls, lack of discipline and the tactical inability to take fortresses resulted in indecisive campaigns. Should an invader manage to amass a superior force, his opponent simply withdrew behind the strong walls of fortifications and waited, perhaps making occasional sallies, until the invading army had exhausted available food from the surrounding countryside. Once the aggressor had used up his resources, he retreated. The defender, with stores of food carefully tucked away behind those walls, generally starved out the invader.

The dean of Carolingian scholars, the late François L. Ganshof, did not share such views concerning the primitive nature of early medieval warfare. He believed that heavy cavalry was decisive in the creation of the Frankish imperium. “Although few in number,” Ganshof wrote, “the units of armored cavalry had an extremely important role, tactical and perhaps strategic: they assured the Carolingian armies of superiority over the Saxons, the Slavs, the Avars, and probably the Danes.” Ganshof, however, left it to his student, J. F. Verbruggen, to formulate a comprehensive view of Carolingian strategy. Although the latter praised the studies of earlier scholars and insisted that Carolingian armies consisted of relatively small contingents of cavalry, Verbruggen also demonstrated that warriors of this period fought as units, that tactical flexibility was possible, and, most importantly, that commanders in the age of Charlemagne were capable of a grand strategy that was based on encircling pincers into enemy territory. Given the current state of research, it is no longer possible to assert that Carolingian warfare was chaotic and backward, and Karl Ferdinand Werner has shown that, on occasions at least, Carolingian armies must have been considerably larger than five thousand troops, which Ferdinand Lot thought was the most that Charlemagne ever had available for mobilization.

The most important critic of the traditional interpretations of Carolingian warfare is Bernard S. Bachrach. While admitting that Carolingian rulers always took care to ensure themselves mounted troops, Bachrach has shown that even the dominance of cavalry in Frankish armies has been grossly exaggerated by scholars at the expense of forces that performed other functions. To demonstrate his point, Bachrach has called attention to the enormous logistic problems that Carolingian commanders dealt with and solved. He wrote:

If any element of Charlemagne’s armies must be identified as tactically decisive and such an exercise is inherently distorting when massive combined operations are undertaken over a period of more than four decades in diverse theaters of operation I would have to suggest that serious consideration be given to the “artillery,” the “engineers,” and those responsible for logistic support. It is inconceivable that such massive fortifications as those at Pavia, Barcelona, or Tortosa could have been taken without a siege train of significant size and sophistication.

As a result of recent studies, a consensus concerning the nature of Carolingian warfare is emerging that stresses the organizational and strategic functions of Charlemagne’s war machine. According to current models, Carolingian conquests began with massive invasions of hostile territory, for which troops were summoned from the various Frankish realms. Carolingian pincers converged on enemy forces from several directions, which divided the energies of the defenders and which eased problems of supply. The objective of these operations was to ravish the opponent’s territory, to drive him from his fortifications, and to establish strategic strongholds from which Frankish garrisons under the command of margraves could assert effective control over the region. Once these tasks had been accomplished, the men constituting this large array returned to Francia for demobilization. From fortresses in occupied territory, smaller units (scarae) could then periodically be sent out by marcher commanders to reconnoiter and to harass resisters. After a region had been conquered, larger armies were necessary only when rebellions threatened the authority of the margraves.

This model of Carolingian warfare is based on the realization that Charlemagne’s accomplishments rested upon strong foundations in the science of war. Military science is social science in that it requires a high degree of social organization to wage war. In the age of Charlemagne, success depended on tactical flexibility, good leadership, careful planning, steadfast perseverance and discipline in the execution of operational plans, and, above all, a sound system of logistics that allowed commanders to achieve battlefield superiority while operating far from their home bases. In spite of the many institutional weaknesses of the Frankish kingdom, Charles Martel, Pepin III, and Charlemagne commanded a formidable military machine that, at its best, was tactically flexible, had a hierarchy of command, and was capable of subjugating enemy territory after prolonged campaigns. Its men had a sense of group purpose, and its commanders were capable of strategic planning. Since it is no longer possible to believe that Carolingian commanders were swashbuckling adventurers who launched campaigns into distant regions without carefully considering operational problems, any study of Carolingian warfare in a given theater must begin with a discussion of the geography of the region under investigation and the tactical and strategic peculiarities presented by that terrain.

Geographic Considerations

Although much of the central Danubian basin was wild and inhospitable in the early Middle Ages, the course of the Danube and its major tributaries, the Drava and the Sava, facilitated the movement of armies from west to east. The frontier lordships that we are considering were mostly organized from Bavaria, but they also included the northern Italian march of Friuli, at least until the end of the third decade of the ninth century. Although forces operating from northern Italy were important in crushing the Avars and in putting down Slavic rebellions, Friuli declined in importance after the disgrace of the margrave Balderic in 828, and Bavaria became the base from which all major military expeditions into the central Danubian basin proceeded.

The importance of Bavaria in Frankish attempts to control this region militarily is rooted in physical and historical geography. Wilhelm Störmer has pointed out that one should not look at ninth-century Bavaria from the point of view of the modern state in the Federal Republic of Germany, for in the early Middle Ages the duchy bearing that name was oriented much more toward south-central Europe than is the current Bundesland. In many ways this southeastern orientation of Carolingian Bavaria was predestined by the formation of the eastern Alps and its great rivers and by the modifications of this natural landscape through the genius of the Romans. Scattered evidence from late Roman and early medieval sources indicates that there was much navigation on the Danube and its major tributaries. In addition, the Bavarians inherited from imperial Rome an excellent network of overland communications, linking the province of Raetia Secunda with southeastern Europe via roads leading through intricate systems of Alpine passes.

In the development of this system of communications, however, the power of imperial Rome bowed to the imposing terrain through which these roads passed. The main roads, which served primarily military purposes, followed courses dictated by rugged Alpine valleys. The structure of the Alps is such that it is difficult to proceed from north to south without ascending two or more passes. The Alps consist of several high ranges separated by deep valleys, cut by the raging torrents of the upper reaches of such great rivers as the Rhone, the Rhine, the Inn, the Enns, the Drava, and the Sava. Because major valleys in the Alps run east-west, they do not facilitate north-south movement. In spite of their reputation for building arrow-straight roads, Roman engineers in the Alps constructed highways conforming to the east-west configurations of the valleys. Even at that, the Romans did not succeed in establishing a system of communications that utilized all of the major Alpine passes over which roads have been constructed since the twelfth century.

The eastern Alps posed formidable problems for the Romans when they tried to establish direct south-north connections from Italy to the Danube. The morphology of the Alps east of the Brenner consists of a series of ridges that radiate outward to the north and to the southeast like the ribs of an open fan, necessitating an intricate system of passes. Although the eastern Alps are not as high or as imposing as their western counterparts, their north-south extension is twice the width of the barrier in the west, requiring a more complicated intra-Alpine network of highways with multiple pass crossings. On the other hand, the difficulties in building roads in this region were somewhat lessened, because gaps between ridges form relatively low passes; however, these mostly connect parallel valleys with east-west orientations, facilitating movement in these directions rather than from south to north or vice versa.

During the early Roman Empire even the Brenner, today the lowest and one of the most accessible passes leading from Italy to the north, had an east-west rather than a south-north orientation. In those days it connected the Inn valley with Venetia, Istria, Pannonia, and the Balkans rather than with the Po plain and, thence, with Rome. In fact, a direct north-south military road (via militaris) over the Brenner did not exist until the desperate circumstances of the third century forced Severi emperors to open one. Earlier commanders and officials had preferred the higher and longer, but more comfortable, via Claudia Augusta that ran northwest from Bolzano to Merano, over the Reschen Pass to the Inn River at Landeck, and then over the Fern Pass to Augsburg. The Bolzano-Innsbruck route over the Brenner was evaded earlier because of a steep defile formed by the Isarco river between Bressanone and Bolzano. Only the necessity of establishing a shorter route to the Danube to Regensburg finally motivated the sustained effort necessary to overcome this geographic obstacle.

Even after the opening of a road linking the Brenner directly to the south, this pass remained a primary avenue of communication with points farther southeast, particularly as pressure increased along the middle Danubian frontier and as Constantinople eclipsed Rome as the first city of the empire. Because of its contemporary function as a main artery from north to south, we tend to forget that the Brenner was for millennia an important conduit for the movement of men, goods, armies, and ideas from east to west and vice versa. Yet such was the case. The Roman roads led from Aquileia on the Adriatic up the valleys of the Piave and the Tagliamento over passes to the Drava in the province of Noricum Mediterraneum. Routes running east-west crossed a narrow divide from the Drava-Gail river system to the Pusteria Valley (beginning near Dobbiaco) whence a gentle descent to Bressanone led ultimately to the Brenner road and to the Inn.

From the vantage of northern Europe, the Brenner led to a network of roads that ran southeast to Sirmium. The important Roman towns on this eastern route through Noricum Mediterraneum were Dobbiaco, Spital, Virunum (near Klagenfurt), Celje, and Ptuj. At each of these locations, the east-west route was joined by roads connecting Venetia and Istria with critical points near the Danube. From Spital, for example, the Severi constructed a road over the Katschberg and Radstädter Tauern passes to the upper Enns. In the Mur Valley this route merged with another one from Klagenfurt via the Gurk Valley and the Turracherhöhe. From the upper Enns a link was established to Salzburg in the province of Noricum Ripense. In addition, the Romans established a second connecting link from Klagenfurt to the Danube by way of Friesach, the low pass near Neumarkt, the Rottmannen Tauern and the Pyhrn passes, and finally terminating either in Wels or in Lorch. From the Drava crossing at Ptuj, an ancient bridge-head, an extremely important road skirted the eastern foothills of the Alps to Szombathely, a crucial junction, whence it branched to the garrison localities of Vienna and Petronel. Another road from Ptuj crossed Pannonia to Budapest via Lake Balaton, where it linked up with one leading from Szombathely to Sirmium by way of Pécs. Finally, an additional route ran southeast from Ptuj following the course of the Drava to Sirmium.

This discussion shows that the roads through Noricum facilitated movement from west to east (and vice versa) rather than from south to north. The roads from the Danube through the Alps via Salzburg or Wels ran southeast toward Pannonia and the Balkans, taking advantage of the west-east contours of such valleys as the Enns, Mur, Gurk, and Drava. From Noricum Ripense all roads did not lead to Rome, many led to Sirmium, and, thence, to Constantinople. The southeastern orientation of roads through the eastern Alps also explains why the bishop of Lorch was in late imperial times the suffragan of the metropolitan of Sirmium.

It is also important to note that there were no Roman roads crossing the Alps east of the Pyhrn Pass. The via militaris from Ljubljana to Vienna ran east of the Vienna Woods. Hence, there were no connecting links between Virunum, the chief city in Noricum Mediterraneum, and those parts of the modern province of Lower Austria between the Enns and the Vienna Woods. Nor was the Semmering Pass, which connects the Mur with the Leitha Valley, traversed by a road in Roman times. The lack of connecting links between the Drava and Lower Austria west of Vienna is due to the physical geography of that region. Although the Alps east of the Enns are not particularly high, they are extremely rugged and inhospitable. Deep gorges and craggy limestone bluffs constituted formidable obstacles to road construction even in later times. Descriptions of the remote character of this region in modern guide books do much to explain why it was bypassed earlier. In fact, it was colonized late and has never supported a large population. Whenever possible the Romans avoided such terrain and constructed their roads through relatively gentle valleys that received ample sunlight, where the inhabitants could support themselves with agriculture and settled husbandry. Only valleys friendly to human habitation could provision large armies on the march.