470 km
This river is called Danube. Its a northern border to Bulgaria and for Romania the south bound.
Danube
This is the river Danube.
Its the Danube river and Danube plain separates Romania and Bulgaria. There are no mountaneous border between the mentioned two countries. And Carpathian mountain range of Romnia or Balkan mountain range (most northern mountains of Bulgaria: none of them serves as border.
This river is Danube (Dunărea).
The River Danube forms the southern border of Romania. The next country to the South is Bulgaria. The River Danube is famous for the waltz of the same name.
the Danube river
This river is Danube.
This river is Danube.
The Danube River forms the border of some countries. They are Romania, Bulgaria, Hungary, Serbia, Slovakia, Austria and Germany.
Romania and Bulgaria border one another and are separated by the Danube. There is no country 'in the middle'.
You think of course to Danube river.