Which capital city is not on the Danube?

The Danube flows southeast passing through four capital cities: Vienna, Bratislava, Budapest, and Belgrade, before emptying into the Black Sea via the Danube Delta in Romania and Ukraine.

The Danube is Europe's second-longest river, after the Volga. It is located in Central and Eastern Europe. It was once a long-standing frontier of the Roman Empire and today flows through 10 countries. The river runs through the largest number of countries in the world (the Nile is second with 9 countries).

Originating in Germany, the Danube flows southeast for 2,850 km (1,770 mi), passing through or bordering Austria, Slovakia, Hungary, Croatia, Serbia, Romania, Bulgaria, Moldova and Ukraine, and its drainage basin extends into nine more countries.

The Danube runs tnrough Bulgaria and several or its cities such as: Vidin, Lom, Kozloduy, Oryahovo and Nikopol, but not through its capital Sofia, which is west of the Iskar river.