Tyumen (tyōmĕnˈyə) [key], city (1989 pop. 477,000), capital of Tyumen region, SW Siberian Russia, on the Tura River. On the Trans-Siberian RR, Tyumen is a major transfer point for river and rail freight. It has shipyards and machine plants. The surrounding area is rich in petroleum and natural gas. Tyumen was founded in 1585 by Yermak and is the oldest city in Siberia. It was formerly an important center of trade with China. The population grew spectacularly with the discover of oil in W. Siberia. The name is sometimes spelled Tiumen.