With a length of 2,857 kilometres, the Danube is the second longest river in Europe after the Volga. The Latin name "Danubius" is probably derived from the Indo-European "dānu" (river). The name Danube applies from the union of the two headwaters Breg and Brigach, which have their source in the Middle Black Forest in the southwest of Baden-Württemberg. As a result, it crosses the large basin landscapes of the northern Alpine foreland and the Vienna Basin (upper reaches), the Pannonian Plain (middle reaches) and the Romanian Lowlands (lower reaches). In an extensive delta, the Danube in Romania flows into the Black Sea. On its course, it crosses the ten riparian states Germany, Austria, Slovakia (Dunaj), Hungary (Duna), Serbia (Dunav) and Romania (Dunărea), which are referred to as the Danube countries, as well as (Donau) berührt.