Astley's Amphitheatre
Astley's Amphitheatre was a performance venue in London opened by Philip Astley in 1773.
Philip AStley opened a theatre in Lambeth in 1773 that became the home of the circus. The original structure was burned down in 1794, but rebuilt, reopening a year later as Astley's Royal Ampthitheatre. The circus was originally 62 feet in diameter, later reduced to 42 feet as being the optimal performance size that allowed attendees a good view, as well as making the best use of centrifugal force to enable Astley's equestrian feats.
The venue had originally begun its life as a riding school, where Astley taught during the morning and performed equestrian tricks in the afternoon, with musical accompaniment provided by his wife. Very soon, Astley began to incorporate other acts, more usually seen at fairs and in London's pleasure garden - acts such as jugglers, acrobats, clowns and strong-men.
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http://www.vam.ac.uk/content/articles/t/the-first-circus/
https://en.wikipedia.org/wiki/Astley%27s_Amphitheatre