So perhaps you're a classical studies scholar and familiar with Roman entertainment, or you've seen "Spartacus" one time and vaguely remember it. Either way, you're probably under the impression that the famous Circus Maximus (the ring where chariot races took place) gave the contemporary circus its name. You're kind of right, in the sense that it's the same word. But that's pretty much where the similarities end.
The first modern circus, founded by Philip Astley in 18th century Britain, was actually referred to as an amphitheatre. In George Speaight's entertaining book "History of the Circus," the author suggests the word was initially adopted because it sounded fancy, which is as good a reason as any. It was only when equestrian showman Charles Hughes decided to perform a show he called "The Royal Circus" did the circus moniker come to be associated with the acts we see today. It probably had nothing to do with the Circus Maximus of ancient Rome but instead was derived from the "circus" ring around Hyde Park where rich people would exercise their horses [source: Speaight]. By the 19th century, "circus" was the accepted nomenclature.