Danube
The Danube flows through many cities, including four national capitals (shown below in bold), more than any other river in the world. Ordered from the source to the mouth they are:
The Danube is navigable by ocean ships from the Black Sea to Brăila in Romania and by river ships to Kelheim, Bavaria, Germany; smaller craft can navigate further upstream to Ulm, Württemberg, Germany. About 60 of its tributaries are also navigable.
Main (river)
The Main is navigable for shipping from its mouth at the Rhine close to Mainz for to Bamberg. Since 1992, the Main has been connected to the Danube via the Rhine-Main-Danube Canal and the highly regulated Altmühl river. The Main has been canalized with 34 large locks () to allow CEMT class V vessels () to navigate the total length of the river. The 16 locks in the adjacent Rhine-Main-Danube Canal and the Danube itself are of the same dimensions.