The backbone of Romania is formed by the Carpathian Mountains, which swing southeastward and then westward through the country. The southern limb of this arc-shaped system is known as the Transylvanian Alps, whose compact, rugged peaks rise to 2,543 m (8,343 ft) in Mt. Moldoveanu, Romania's highest. The eastern Carpathians have an average elevation of 1,000 m (3,300 ft) and exceed 1,900 m (6,200 ft) only in the highest ranges. On the eastern and southern fringes of the Carpathian arc are the low plateaus and plains of Walachia, extending to the Prut River (Moldovan border) in the east and to the Danube (Bulgarian border) in the south. On the inside of the Carpathian arc is the Transylvanian Basin, a hilly region dissected by the wide, deep valleys of the Mures and Somes rivers. The Dobruja, located between the lower Danube and the Black Sea, is an eroded plateau with average elevations of 400 to 600 m (1,310–1,970 ft). Except for the low-lying, swampy Danube Delta in the north, the Black Sea coast of the Dobruja is steep, facing the sea with almost vertical cliffs.
Romania is susceptible to severe earthquakes. An earthquake that struck Romania on 4 March 1977 destroyed or severely damaged some 33,000 buildings and left more than 34,000 families homeless. The shock, measuring 7.2 on the open-ended Richter scale, was the most severe in Europe since a series of shocks in October–November 1940, also in Romania.