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.
Commissions of the Danube River
In 1938, a committee of experts inspected the Sulina and found it was almost impassable by that time. And in August of that same year, the regime of the two commissions was swept away by rise of German power on the river. A series of treaties put control in the hands of the Germans, who maintained it until the Nazi retreat in 1944 and ultimate defeat in 1945. In 1948 a Danube river conference was held, and a new treaty was adopted, putting governance of the river under commissions composed only of the riparian powers, ending more than four decades of Western European presence in the control of the important waterway.