The Frankish military response to the Northmen under Charles the Bald cansisted primarily of fortified bridge construction to inderdict the passage of Norse ships on the fluvial systems of West Francia. Previous scholars, namely Ferdinand Lot and Fernand Vercauteren, provided chronological narratives of this process, while Kurt Ulrich Jäschke undertook a three-way comparison of the West Frankish military measures with the fortified burghs of Alfred the Great and the defence works of Henry I of Saxony. Departing radically from these approaches this study on the logistics of the entire bridge-building process promises to develop data on the expenditure of material resources on the project, and will illuminate the complexity of this Carolingian administrative effort with an analysis of texts on the organisation of the labour for this project. The methodology of this study involves the integration of several different kinds of evidence, specifically, the written texts, archaeological findings, historical climatology and modem comparative data on human and animal efficiency. This interdisciplinary approach, when combined with similar studies of this kind, will provide the basis for an environmental history of Early Mediaeval Europe.

The fortified bridges of Charles the Bald represent a turning-point in the history of mediaeval bridges and fortifications. Not until the 860s were bridges built on extensive fluvial systems for the unique military purpose of fluvial defence. Charles the Bald seems to have stumbled upon the idea of the fortified bridge during a military operation in 862, when he found a way to stop the Northmen by cutting off their retreat on the Mame with a hastily fortified bridge, and then decided to expand on this discovery with a project to build a fortified bridge at Pont de I’Arche to prevent further Norse incursions on the Seine. Until that time, bridges had functioned in combination with roads to facilitate overland transport. Not a simple repair job on the ald wreckage, the new bridge on the Marne was rebuilt differently (secus) from its original construction. The sense of the passage in the Annales Bertiniani indicates that the king repaired and fortified the partially destroyed bridge on the Marne, since the renovated bridge successfully cut off the Norse retreat downstream from Meaux.