The Danube is the European Union's longest and the continent's second longest river. 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, 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 10 countries. The Danube basin was the site of some of the earliest human cultures. The Danubian Neolithic cultures include the Linear Pottery cultures of the mid-Danube basin.