The Danube is a river in Central Europe, the continent’s second longest after the Volga. Classified as an international waterway, it originates in the town of Donaueschingen which is in the Black Forest of Germany at the confluence of the rivers Brigach and Breg. The Danube then flows southeast for 2,872 km (1,785 mi), passing through four Central European capitals before emptying into the Black Sea via the Danube Delta in Romania and Ukraine. Once a long-standing frontier of the Roman Empire, the river passes through or touches the borders of ten countries: Romania (29.0% of basin area), Hungary (11.6%), Serbia (10.2%), Austria (10.0%), Germany (7.0%), Bulgaria (5.9%), Slovakia (5.9%), Croatia (4.4%), Ukraine (3.8%), and Moldova (1.6%). Its drainage basin extends into nine more.