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.
Danube–Black Sea Canal
The construction plans for the canal took a different turn with the signing of the Treaty of Paris on March 30, 1856, ending the war. Russia ceded the Danube mouths to the Ottomans and southern Bessarabia (lately organised as the Cahul, Bolgrad and Ismail counties) to their vassal, Moldavia. The freedom of international navigation on the Danube was restored; passage taxes were canceled, police and quarantine rules were simplified; and the European Commission of the Danube was established, with representatives of 7 powers: Britain, France, Austria, Russia, the Ottoman Empire, the Kingdom of Prussia, and the Kingdom of Sardinia. The Commission was responsible for the clearing of the Danube mouths from deposits of the river, and when necessary with clearing natural barriers, with the goal of ensuring of good conditions for navigation. The effect was that Austria, Britain, and France changed their attitude to the project for a Danube-Black Sea canal. The newspaper "Zimbrul" announced on May 25, 1856 that the plan for building the canal was abandoned; instead a railroad line Cernavodă – Constanța was to be built. After two and a half years of construction, the latter was inaugurated on October 4, 1860. Following the building of a railway connection in 1860, goods were easily and inexpensively transported from Constanța by rail, so plans for a canal were again abandoned.