Rhine-Main-Danube-Canal: The idea of linking the Danube and Rhine rivers had already been conceived by Charlemagne in 793. In the 19th century, King Ludwig I of Bavaria had a 173-kilometre-long canal (Ludwig-Main-Donau Canal) built from Kehlheim to Bamberg, which was, however, rather narrow and difficult to negotiate because of its 100 locks. The canal was finally closed in 1945 as a result of war damage. In 1921, the Rhein-Main-Donau AG was founded and charged with the reconstruction of the canal. When a 171-kilometre-long waterway from Bamberg to Kehlheim was opened to navigation on September 25, 1992, a 3,500-kilometre-long waterway linking the North Sea to the Black Sea was created. The canal has a cross-section of 55 by 4 metres; differences in height are overcome by means of 16 locks. The Rhine-Main-Danube Canal has also greatly improved the possibilities of shipping on the Danube for Austria.