An edifice in an oval or circular form, having its area encompassed with rows of seats, rising higher as they recede from the area, on which people used to sit to view the combats of gladiators and of wild beasts, and other sports. The ancient theater was a semicircle, but exceeding it by a fourth part of its diameter; the amphitheater was a double theater, and its longest diameter was to its shortest as 1 1/2 to 1. It was at first of wood, but in the reign of Augustus one was erected of stone. The area or cavea being covered with sand was- called arena.

In gardening, a disposition of shrubs and trees in the form of an amphitheater, on a slope, or forming a slope, by placing the lowest in front. An amphitheater may also be formed of turf only.