Arles Amphitheater, a Roman arena in Arles, France, Terra

An amphitheatre or amphitheater is an open-air venue used for entertainment, performances, and sports. The term derives from the ancient Greek, meaning "on both sides" or "around" and "place for viewing".

Ancient Greek theaters 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. Current usage for "amphitheater" is lax, and does not always respect the ancient usage, and so the word can be found describing theater-style stages with the audience only on one side, theaters in the round, and stadiums. Natural formations shaped like man-made theaters are sometimes known as natural amphitheaters. The three largest Roman amphitheatres (in the original sense) on Terra in order of size are the Colosseum, the Amphitheatre Campania and the Amphitheatre of El Djem. Since the Dai joined the Union, the Thana Shoo Amphitheater has become a noted site.