Portion of a theater or hall where an audience sits, as distinct from the stage. The auditorium originated in the theaters of ancient Greece, as a semicircular seating area cut into a hillside. Floor levels in a large auditorium may include stalls, private boxes, dress circle, balcony or upper circle, and gallery. A sloping floor and converging walls allow for a clear view of the stage and improve acoustics. The walls and ceilings of contemporary auditoriums usually conceal light, sound, and air-conditioning equipment.