Charlemagne's Summit Canal: An Early Medieval Hydro-Engineering Project for Passing the Central European Watershed

Abstract

The Central European Watershed divides the Rhine-Main catchment and the Danube catchment. In the Early Medieval period, when ships were important means of transportation, Charlemagne decided to link both catchments by the construction of a canal connecting the Schwabian Rezat and the Altmühl rivers. The artificial waterway would provide a continuous inland navigation route from the North Sea to the Black Sea. The shortcut is known as Fossa Carolina and represents one of the most important Early Medieval engineering achievements in Europe. Despite the important geostrategic relevance of the construction it is not clarified whether the canal was actually used as a navigation waterway. We present new geophysical data and in situ findings from the trench fills that prove for the first time a total length of the constructed Carolingian canal of at least 2300 metres. We have evidence for a conceptual width of the artificial water course between 5 and 6 metres and a water depth of at least 60 to 80 cm. This allows a crossing way passage of Carolingian cargo scows with a payload of several tons. There is strong evidence for clayey to silty layers in the trench fills which reveal suspension load limited stillwater deposition and, therefore, the evidence of former Carolingian and post-Carolingian ponds. These findings are strongly supported by numerous sapropel layers within the trench fills. Our results presented in this study indicate an extraordinarily advanced construction level of the known course of the canal. Here, the excavated levels of Carolingian trench bottoms were generally sufficient for the efficient construction of stepped ponds and prove a final concept for a summit canal. We have evidence for the artificial Carolingian dislocation of the watershed and assume a sophisticated Early Medieval hydrological engineering concept for supplying the summit of the canal with adequate water.

Genesis of magnetic anomalies and magnetic properties of archaeological sediments in floodplain wetlands of the Fossa Carolina

“…Nevertheless, the canal was never finished (Kirchner et al, ) and only remains of it are visible today (Schmidt et al, ; Schmidt, Werther, & Zielhofer, ). The post‐Carolingian canal filling was reconstructed using excavation, drillings, and sediment analysis (Völlmer et al, ; Zielhofer et al, ).…”

“…The valley fills consist of Pleistocene sandy to loamy fluvial sediments. The canal has a length of 2.9 km, as proven by drillings (Kirchner et al, ; Zielhofer et al, ), archaeological excavation (Werther et al, ), and direct‐push sensing (Hausmann et al, ; Völlmer et al, ). Furthermore, extensive multi‐disciplinary research has been carried out at the Early Medieval canal over the last decade (Ettel, Daim, Berg‐Hobohm, Werther, & Zielhofer, ; Hausmann et al, ; Kirchner et al, ; Linzen et al, ; Schmidt et al, ; Schmidt et al, ; Stele, ; Zielhofer et al, ).…”

“…Two sections of the Fossa Carolina floodplain were selected for our study: the West–East Section and the Northern Section (Zielhofer et al, ) (Figure ). Both sections are located in the foothills of the Weissenburger Alb of the southern Franconian Jura (Jätzold, ) at an elevation of 413 to 420 m above sea level.…”

“…Both sections are located in the foothills of the Weissenburger Alb of the southern Franconian Jura (Jätzold, ) at an elevation of 413 to 420 m above sea level. They are situated in water sensitive areas and covered by bogs, floodplain gley soils, and colluvial deposits (LfU‐WMS, ; Zielhofer et al, ). The sections are divided by the current watershed.…”

“…Man‐made magnetic anomalies have been found at several sites in river floodplains (Weston, ), including Fossa Carolina (Zielhofer et al, ). So far, the genesis of these anomalies has only been discussed in general terms without considering the physical properties of floodplain sediments.…”