A traditional yurt (from the Turkics) or ger (Mongolian) is a portable, round tent covered with skins or felt and used as a dwelling by nomads in the steppes of Central Asia. The structure comprises an angled assembly or latticework of pieces of wood or bamboo for walls, a door frame, ribs (poles, rafters), and a wheel (crown, compression ring) possibly steam-bent. The roof structure is often self-supporting, but large yurts may have interior posts supporting the crown. The top of the wall of self-supporting yurts is prevented from spreading by means of a tension band which opposes the force of the roof ribs. Modern yurts may be permanently built on a wooden platform; they may use modern materials such as steam-bent wooden framing or metal framing, canvas or tarpaulin, Plexiglas dome, wire rope, or radiant insulation.