amphitheatre

noun

1. An open, outdoor theatre (which may be a theatre in the round, or have a stage with seating on only one side), especially one from the classical period of ancient Greece or Rome, or a modern venue of similar design.

   “Ancient Roman amphitheatres were mostly oval or circular in plan, with seating tiers that surrounded the central performance area, like a modern open-air stadium.”

   “We had previously visited the building prepared for the assemblage, which was a vast pentagonal semicircular amphitheatre of painted wood and canvas work, ...”

   “The dry quarry in Shrewsbury [was] in use from at least 1445-6 [...until] 1568-9 (and perhaps beyond)[. ...] Location of this as the site of a semicircular amphitheatre [used in the 1400s and 1500s] is confirmed by the evidence, published in total for the first time in the present volume.”

2. A natural formation of a similar shape, where a steep mountain or slope or particular rock formation forms a partial or complete bowl, especially one used as a performance space (and possibly modified by carving out seats, etc) because the slopes naturally amplify or echo sound.

   “The difference between the approach to Baylen from the west and from the east, is that on the former side the traveller reaches the town through a semicircular amphitheatre of upland, while by the latter he comes up a V-shaped valley ...”

   “Brecon or Aberhonddu, a typical Welsh town of 5,350 inhabitants, stands in a grand amphitheatre of hills and mountains at the confluence of the rivers Usk, Honddu, and Tarell.”