In 1762 the St.Just 'Plen an Guary' was described by William Borlase, historian and vicar of St Just, as "an exact circle of 126 feet diameter; the perpendicular height of the bank, from the area within, now seven feet, but the height from the bottom of the ditch without, ten feet at present, formerly more. The seats consist of six steps, fourteen inches wide, and one foot high, with one on the top of all where the rampart is about seven feet wide."
Another famous Cornish round is Perran's Round near Perranporth.
Gwennap Pit has also been used to stage plays though this came to prominence in the 18th & 19th centuries when it was used by the Methodist preachers for their open air services.
The major Theatre in Cornwall is still an open air one - the Minack Theatre at Porthcurno. However in recent years Cornwall has built its own Hall for Cornwall in the old City Hall in Truro which has a varied programme of events throughout the year.