In Ancient Rome, a “circus” was an oblong arena where events like chariot races, games, and other performances were held. As you might guess, the Circus Maximus was - in a word - huge. It was the Roman Empire’s largest stadium, measuring more than 2,000 feet long by 387 feet wide and capable of holding an audience of 150,000.
First built in the 6th century B.C.E., the Circus Maximus was expanded over the next several centuries (and rebuilt occasionally after fire and flood damaged), until it was rebuilt by Emperor Trajan in the early 2nd century AD. In addition to chariot and horse races, the Circus Maximus also held religious ceremonies, and parades.
The last recorded uses of the Circus Maximus are in the 6th century AD, and today there’s very little left of the structures. The site is now a public park, and you can see the overall oblong shape where the Circus used to be, as well as some of the starting gates.