have turned the rocks into spectacular figures such as the Sphinx and Babele. The region was crisscrossed by an ancient network of trans-Carpathian roads, and vestiges of the old Roman Way are still visible. Numerous passes and the valleys of the Olt, Jiu, and Danube rivers provide routes for roads and railways through the mountains. The Western Romanian Carpathians are the lowest of the three ranges and are fragmented by many deep structural depressions. They have historically functioned as "gates," which allow easy passage but can be readily defended. The most famous of these is the Iron Gate on the Danube. The Western Romanian Carpathians are the most densely settled, and it is in the northernmost area of this range, the Apuseni Mountains, that permanent settlements can be found at the highest altitudes. Enclosed within the great arc of the Carpathians lie the undulating plains and low hills of the Transylvanian Plateau—the largest tableland in the country and the center of Romania. This important agricultural region also contains large deposits of methane gas and salt. To the south and east of the Carpathians, the Sub-Carpathians form a fringe of rolling terrain ranging from 396 to 1,006 meters in elevation. This terrain is matched in the west by the slightly lower Western Hills. The symmetry of Romania's relief continues with the Getic Tableland to the south of the Sub-Carpathians, the Moldavian Tableland in the east between the Sub-Carpathians and the Prut River, and the Dobrujan Tableland in the southeast between the Danube and the Black Sea. The Sub-Carpathians and the tableland areas provide good conditions for human settlement and are important areas for fruit growing, viticulture, and other agricultural activity. They also contain large deposits of brown coal and natural gas. Beyond the Carpathian foothills and tablelands, the plains spread south and west. In the southern parts of the country, the lower Danube Plain is divided by the Olt River; east of the river lies the Wallachian Plain (including the strategically important Focșani Gate), and to the west is the Oltenian or Western Plain. The land here is rich with chernozemic soils and forms Romania's most important farming region. Irrigation is widely used, and marshlands in the Danube's floodplain have been diked and drained to provide additional tillable land. Romania's lowest land is found on the northern edge of the Dobruja region in the Danube Delta. The delta is a triangular