The Danube River

The Danube is the second longest river in Europe (the Volga is the longest).

Danube River map from Encyclopedia Britannica

The Danube begins in Western Germany, in the Black Forest Mountains, and flows for 1,770 miles to the Black Sea. 

It's known by different names in the nine countries it travels through:

Germany	Donau
Austria
Slovakia	Dunaj
Hungary	Duna
Croatia	Dunav
Serbia
Bulgaria
Romania	Dunarea
Ukraine	Dunai

Source:  www.britannica.com