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.
Nazi rule over the Danube River
Nazi Germany's main concerns in establishing control over the Danubian basin were economic in nature. Adolf Hitler's primary objective throughout the war was to conquer sufficient "living space" ("Lebensraum") at the expense of the Soviet Union in Eastern Europe for German settlement, which would in turn allow control over the country's rich deposits of natural resources (such as oil, grain and iron), transforming Germany into an economic autarky. The Danube was considered to be the main route along which this stream of raw materials was to be transported to Germany proper. Hitler referred to the Danube as the "river of the future". At other times he was more explicit about its role in the German-dominated Europe: