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
The European Commission of the Danube, the CED, continued functioning during at least the first two years of the war, and delegates from the Allies and the Central Powers continued to meet together. After Germany attacked Romania in 1916, the Central Powers (Germany, Austria-Hungary, Bulgaria, and Turkey) kept the commission in operation for a short time — but without the British and the French. Indeed, the Germans attempted to legalize a commission that would have perpetually excluded the Allied powers. on May 7, 1918, they concluded a separate peace with the Romanians, changing the EDC into a Commission of the Mouth of the Danube; its competence was maintained, but membership was restricted to Danubian or Black Sea countries; above Braila, control was to be "in the hands of the countries bordering the river", that is, Romania, Bulgaria, Serbia, Austria, and Germany. Germany, Austria-Hungary, Bulgaria, Turkey, and Rumania obtained the right to keep warships on the river; this led, as a reaction, to the internationalization of the river between Ulm and the Black Sea after the war. The same stipulations were included in the peace treaty between Germany and Russia in 1918.