Circus

Chariot racing was Rome's oldest and most popular pastime, dating back to at least the Roman monarchy.
Greek chariot races were held in hippodromes in the east, but in the west they were held in circuses. Other events eventually infiltrated the circus games (ludi circenses), such as Greek athletics and wrestling, but chariot racing remained the popular favorite. As a sport, it was highly expensive, but organized into a highly profitable business. There were four chariot facing factions, the blues, greens, whites, and reds, the colors of which were worn by respective charioteers during races. If successful, a charioteer could become rich and famous throughout Rome. Images of charioteers survive in sculpture, mosaic, and molded glassware, sometimes even with inscribed names. The factions rivaled greatly, sometimes leading to violence among supporters. In general, however, the greens and blues were the favorites.

The circus itself consisted of tiers of seats build around a U-shaped arena with an elaborately ornamented barrier, the spina, running down the middle. Metae, or turning posts, adorned each end of the course. At the open end of the U waited up to twelve four horse chariots (quadrigae), which began the race from starting gates (carceres), drove to the right of the spina, and then continued counter-clockwise for seven laps. At each end of the spina were seven lap markers, one of which was removed after each lap run by the charioteers. Circuses were also used for two horse chariot racing (bigae), and by the late republic other events, such as foot and horse racing, athletics, and gladiatorial shows/mock battles were commonplace in the circus.

 Excerpted from http://library.thinkquest.org/26602/entertainment.htm