An amphitheatre or amphitheater  is an open-air venue used for entertainment, performances, and sports. The term derives from the ancient Greek (amphitheatron), from ? (amphi), meaning "on both sides" or "around" and ? (thé?tron), meaning "place for viewing".
Ancient Roman amphitheatres were oval or circular in plan, with seating tiers that surrounded the central performance area, like a modern open-air stadium. In contrast both ancient Greek and ancient Roman theatres were built in a semicircle, with tiered seating rising on one side of the performance area. In modern usage, an "amphitheatre" may consist of theatre-style stages with spectator seating on only one side, theatres in the round, and stadia. Natural formations of similar shape are sometimes known as natural amphitheatres.
Ancient Roman amphitheatres were major public venues, circular or oval in plan, with perimeter seating tiers. They were used for events such as gladiator combats, chariot races, venationes (animal hunts) 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 more or less semicircular in shape; from the circuses (similar 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 1st 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. The most elaborate featured multi-storeyed, arcaded façades and were elaborately decorated with marble, stucco and statuary. After the end of gladiatorial games in the 5th century and of staged animal hunts in the 6th, most amphitheatres fell into disrepair. Their materials were mined or recycled. Some were razed, and others were converted into fortifications. A few continued as convenient open meeting places; in some of these, churches were sited.
In modern usage, an amphitheatre is a circular, semicircular or curved, acoustically vibrant performance space, particularly one located outdoors. Contemporary amphitheatres often include standing structures, called bandshells, sometimes curved or bowl-shaped, both behind the stage and behind the audience, creating an area which echoes or amplifies sound, making the amphitheatre ideal for musical or theatrical performances. Small-scale amphitheatres can serve to host outdoor local community performances.
Notable modern amphitheatres include the Shoreline Amphitheatre, the Hollywood Bowl and the Aula Magna at Stockholm University. The term "amphitheatre" is also used for some indoor venues such as the Gibson Amphitheatre.
A natural amphitheatre is a performance space located in a spot where a steep mountain or a particular rock formation naturally amplifies or echoes sound, making it ideal for musical and theatrical performances. An amphitheatre can be naturally occurring formations which would be ideal for this purpose, even if no theatre has been constructed there.
Notable natural amphitheatres include the Drakensberg amphitheatre in Drakensberg, South Africa, Slane Castle in Ireland, the Supernatural Amphitheatre in Victoria, Australia, Ruth Amphitheatre in Alaska, Echo amphitheatre, Red Rocks Amphitheatre in Morrison, Colorado and The Gorge Amphitheatre in Washington State, United States.