Fossa Carolina

[1] Carolingian sources report that Frankish king Charlemagne gave orders to dig a 2 kilometers long canal from Treuchtlingen to Weißenburg in Bayern in 793.

According to Einhard, writing around two decades later, Charlemagne was convinced by "supposed experts" that it would be possible to travel in comfort by ship from Rhine to Danube if the Rezat could be linked to the Altmühl.

The king assembled a large number of workers and in person supervised construction in the fall of 793 of a 2,000 step long and 300 feet wide moat.

Einhard reports that the project failed due to the marshy ground and continuous rainfall, which caused excavated material to slide back.

Heaps of excavated earth that delineate the canal's banks stretch further, totalling around 1.2 km (0.75 mi); in places they rise up to 10 m (33 ft) in height.