The circus was invented in the 1760s by a British cavalry officer, Philip Astley, who started with trick riding, moved on to "hippodrama" (plays in which horses took center stage) and established many of the basics of circuses, including brass-band marching tunes, a broad center ring and even the "big top" itself.
WSJ: Week in Words: Susceptor, Laminar, Hippodrama, Ogooglebar