 The Danube forms a natural border between Muntenia and Dobruja.The west-central region, known as Transylvania, is delimited by the arc of the Carpathians, which separates it from the Maramureș region in the northwest; by the Crișana area, which borders Hungary in the west; and by the Banat region of the southwest, which adjoins both Hungary and Serbia.It is these areas west of the Carpathians that contain the highest concentrations of the nation's largest ethnic minorities—Hungarians, Germans, and Serbs.