The name amphitheatre (alternatively amphitheater) refers to a level, open space surrounded by an oval area that gradually ascends. The area may be a man-made structure or a natural geographic formation, but it is suited for seating people on the sloping area for the viewing of spectator sports, games, concerts, displays, rallies, or theatrical performances. Today we might call it a theater-in-the-round. An amphitheatre can be classified as either an ancient amphitheatre, a contemporary amphitheatre, or a natural amphitheatre, being particularly associated with ancient Rome and ancient Greece. Amphitheatres were used for various types of public events.

Ancient Roman amphitheatres were circular or oval in shape, and used for events such as gladiator combats, chariot races, venationes (animal slayings) and executions. About 230 Roman amphitheatres have been found across the area of the Roman Empire. Their typical shape, functions and name distinguish them from Roman theatres, which are usually semicircular in shape; from the circuses (akin to hippodromes) whose much longer circuits were designed mainly for horse or chariot racing events; and from the smaller stadia, which were primarily designed for athletics and footraces.

The earliest Roman amphitheatres date from the middle of the first century BC, but most were built under Imperial rule, from the Augustan period (27 BC-14 AD) onwards. Imperial amphitheatres were built throughout the Roman empire; the largest could accommodate 40,000-60,000 spectators, and the most elaborate featured multi-storied, arcaded facades and were elaborately decorated with marble, stucco and statuary. After the end of gladiatorial games in the 5th century and of animal killings in the sixth, most amphitheatres fell into disrepair, and their materials were mined or recycled. Some were razed, and others converted into fortifications. A few continued as convenient open meeting places; in some of these, churches were sited.

The best-known amphitheatre in the world is the Roman Colosseum, which is more correctly termed the Flavian amphitheatre (Amphitheatrum Flavium), after the Flavian dynasty who had it built.