An amphitheatre or amphitheater is an open-air venue used for entertainment, performances, and sports. The term derives from the ancient Greek ἀμφιθέατρον, from ἀμφί, meaning "on both sides" or "around" and θέατρον, meaning "place for viewing". Ancient Greek theatres were built in a semicircle, with tiered seating above a performance area. Ancient Roman amphitheatres were oval or circular in plan, with seating tiers that surrounded the central performance area, like a modern open-air stadium. Modern usage for "amphitheater" does not always respect the ancient usage, and so the word can embrace theatre-style stages with the audience only on one side, theatres in the round, and stadiums. Natural formations shaped like man-made theatres or amphitheatres are sometimes known as natural amphitheatres. The three largest Roman amphitheatres in the world in order of size are the Colosseum, the Amphitheatre Campania and the Amphitheatre of El Djem.