An architectural feature found in many prehistoric Anasazi communities in the Southwestern United States. Usually a circular, subterranean structure, kivas were and are used for a combination of both spiritual and social purposes. Roofs , which provided an access by a ladder in the center, were constructed of beams and mud supported by pilasters. Stone benches lined the inside wall and a hole in the floor called a sipapu symbolized the connection to the lower world and the birth place through which life entered to this world. A ventilation shaft allowed floor-level air to fuel a fire pit in the center of the kiva. Contempory kivas used by Hopi peoples are usually square or D-shaped structures used for the same purposes as earlier but are constructed above-ground.