The Danube ( , also known by other names) is the European Union’s longest river, located in Central and Eastern Europe. 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 , passing through four capital cities 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.