 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.