Frankish Frontiers and Defence

Between about 450 and 900, the Frankish world extended across western and central Europe, but rulers’ reach depended on local relationships as much as campaigns. A frontier could be a contested town, a border region entrusted to a commander, or a river crossing that controlled movement. The Merovingian kings who ruled before 751 and the Carolingian dynasty that followed faced these questions through different political arrangements.

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Merovingian kingdoms and contested towns

The Merovingian Franks established themselves in former Roman territories and extended their rule into Aquitaine, Burgundy and lands east of the Rhine. After Clovis died in 511, his sons divided the kingdom, and later generations repeatedly rearranged the dynastic shares. Aquitaine, in what is now southwestern France, was a region of competing royal claims: Frankish conquest expelled the Visigoths in 507, yet royal authority continued to depend on local rulers and political ties.

Tours, on the Loire in central France, shows how control mattered inside a kingdom as well as at its outer edge. In the sixth century, rivalry among Merovingian kings and their supporters affected the town’s count, a royal regional official, and its bishop, a local church leader. Both royal factions were connected to the cult of Saint Martin, whose shrine and monastery held land and wealth. The town’s religious institutions and local offices made control of Tours important to competing rulers.

Carolingian rule and the marches

Under the Frankish king Charlemagne (r. 768–814), Carolingian rulers expanded through conquest but also relied on submission, hostages and regional officials. A “march” was a border region where a ruler assigned a commander responsibility for holding the frontier and managing relations with neighbouring peoples. Charlemagne’s imperial coronation in 800 belonged to this period; the Holy Roman Empire conventionally dated from 962 was a later political formation. Einhard, a ninth-century court biographer, identifies Roland as governor of the March of Brittany, on the Atlantic coast of western France, a frontier office. On the Saxon border in northern Germany, he says forests and ridges marked only a few stretches, while most of the boundary ran through open country. Raids and reprisals fed a war lasting from 772 to 804, in which hostages and renewed submissions accompanied repeated campaigns. In Bavaria, in southern Germany, Duke Tassilo submitted to Charlemagne in 787 and gave hostages, including his son; after Tassilo was removed in 788, counts governed the province.

On the southern edge, the Spanish March developed in lands around the eastern Pyrenees, in present-day northeastern Spain and southwestern France. Charlemagne’s 778 expedition failed to take Zaragoza in northeastern Spain, but later campaigns and local submissions established Frankish counties north and south of the mountains. Counts governed these districts, while royal grants to settlers and monasteries helped connect distant communities to the court. The frontier was therefore maintained through local landholding and political loyalty as well as warfare. The Spanish March remained part of wider imperial politics, and its counts negotiated with kings over authority and service.

Fortified places and exposed routes

Charlemagne’s campaign in Aquitaine offers a concrete example of a fort serving a political purpose. After Hunold fled across the Garonne, Einhard says Charles built a fort at Fronsac, near the Dordogne, then demanded that the duke of Gascony surrender the fugitive. The duke yielded Hunold and submitted his province.

Rivers and coastlines were both routes into the realm and corridors for Frankish forces. Einhard reports that Charlemagne prepared against Northmen, Scandinavian raiders often called Vikings, by building ships on rivers flowing into the North Sea and stationing watches in harbours and at river mouths large enough for vessels. He also describes coastal watches in southern Gaul and Italy against Muslim raiders. His account records that raiders still sacked the Italian town of Civita Vecchia and attacked Frisian islands in the southern North Sea, even while presenting Charlemagne’s precautions as effective.

Bridges and ninth-century defence

In 862, Viking ships sailed up the Marne to Meaux, east of Paris. Charles the Bald, king of West Francia, moved to intercept them, but the bridges had been destroyed and the raiders had seized the ships. He rebuilt a bridge to an island near Trilbardou, cutting off their route downstream, and posted armed groups on both banks. The Vikings then gave hostages and agreed to return captives taken along the river before withdrawing. In this case a bridge was not only a crossing: its position helped close a waterway and support negotiations.

The following year, Charles gathered leading men, workmen and carts at Pîtres, where the Andelle and Eure join the Seine, and ordered fortifications built to stop ships moving up or down the river. The Pîtres works were a more sustained project than the hastily rebuilt Marne bridge of 862, requiring coordinated labour and transport.