Transdanubia (; , or , ) is a traditional region of Hungary. It is also referred to as Hungarian Pannonia, or Pannonian Hungary. Administrative divisions Traditional interpretation The borders of Transdanubia are the Danube River (north and east), the Drava and Mura rivers (south), and the foothills of the Alps roughly along the border between Hungary and Austria (west). Transdanubia comprises the counties of Győr-Moson-Sopron, Komárom-Esztergom, Fejér, Veszprém, Vas, Zala, Somogy, Tolna, Baranya and the part of Pest that lies west of the Danube. (In the early Middle Ages the latter was known as Pilis county.) This article deals with Transdanubia in this geographical meaning. Territorial changes While the northern, eastern and southern borders of the region are clearly marked by the Danube and Drava rivers, the western border was always identical with the political boundary of Hungary, therefore it was affected by the territorial changes of the 20th century. Before the Treaty of Trianon in 1920 the present-day regions of Burgenland, Prekmurje and Međimurje were integral parts of Transdanubia. The three villages of Rusovce, Jarovce and Čunovo also belonged to Transdanubia before the Paris Peace Treaty in 1947. Transdanubia is essentially a Hungarian geographical concept so these areas ceased to be parts of it when they were annexed by neighbouring countries. EU regions Transdanubia is a NUTS territorial unit in the European Union, consisting of Central Transdanubia, Western Transdanubia and Southern Transdanubia (see NUTS:HU). Pest county and Budapest belong to the region of Central Hungary. It has an area of 37,000 km2 and a population of around 3.1 million. Geography The territory of the region is 38,000 km², and it comprises almost half of the whole territory of Hungary. In terms of historical geography it also comprised major part of northern Pannonia, and thus the term Hungarian Pannonia refers to this region. The terrain is very varied with gentle hills, valleys, basins, mountains and plains. The main geographical formations are the Transdanubian Mountains, the southern half of the Little Alföld, the Alpokalja, the Transdanubian Hills, and the Mezőföld (part of the Great Alföld). The main rivers are the Danube, Drava, Rába, Zala, and Kapos. In the middle of Transdanubia lies the biggest freshwater lake of Central Europe, the Lake Balaton. Other importants lakes are the Lake Velence and the Lake Fertő. History Historically the counties of Transdanubia were Moson, Győr, Sopron, Vas, Zala, Veszprém, Fejér, Komárom, Esztergom, Somogy, Tolna