<Tr> <Th> Cities </Th> <Td> Ulm, Ingolstadt, Regensburg, Linz, Vienna, Bratislava, Győr, Budapest, Dunaújváros, Vukovar, Novi Sad, Zemun, Belgrade, Pančevo, Smederevo, Drobeta Turnu - Severin </Td> </Tr> <Tr> <Th> Primary source </Th> <Td> Breg </Td> </Tr> <Tr> <Td> - location </Td> <Td> Martinskapelle, Black Forest, Germany </Td> </Tr> <Tr> <Td> - elevation </Td> <Td> 1,078 m (3,537 ft) </Td> </Tr>

What name is given to the danube river plain surrounded by mountains