The Fossa Carolina was a navigable channel in what is today the German state of Bavaria, intended to connect the Swabian Rezat river to the Altmühl river . It was created during the early Middle Ages, long before the Ludwig Canal and the Rhine-Main-Danube Canal. If it was indeed operational, this channel would have been the first to link the Rhine basin to the Danube basin, across the European Watershed.
In 793 Charlemagne gave orders to dig a 3 kilometers long channel from Treuchtlingen to Weißenburg in Bayern. It seems that the goal of this work was to improve the transportation of goods between the Rhineland and Bavaria. Another theory claims that the main purpose was to bring back Charlemagne's war vessels from the Danube to the Rhine.
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