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
By 1935, a new power had appeared through the entire length of the Danube — Nazi Germany, whose new self-propelled barges swiftly moved up and down the river outside Germany's borders, "the pioneers of the new order. They flew the Swastika and were built of bullet-proof steel."