a large river that flows west to east, through Germany, Austria, Slovakia, Hungary, Yugoslavia, Croatia, Serbia, Bulgaria, and Romania, emptying into the Black Sea. Vienna, Budapest, and Belgrade are on the Danube. The Danube is the second-longest river in Europe.
The Danube (ancient Danuvius, ancient Greek Istros) is the longest river in the European Union and Europe's second-longest (after the Volga). It originates in the Black Forest in Germany as two smaller rivers—the Brigach and the Breg—which join at Donaueschingen; it is from this point that it is known as the Danube. The river flows eastwards for a distance of some 2850 km (1771 miles), passing through several Central and Eastern European capitals, before emptying into the Black Sea via the Danube Delta in Romania.