Antique Roman hippodrome or horse racing stadium, probably the largest sports arena ever constructed.

The origins of the stadium is from around 500 BC and was - according to tradition - built by King Tarquinius Priscus, and then improved and enlarged several times over the centuries. It was placed in the valley between Palatine and Aventine – two of the ancient seven hills of Rome – where the hillsides offered natural seating for the audience. Later on, almost every emperor added something of his own to the stadium.

The name Circus is the Latin word for circle, but Circus Maximus was more shaped like a horseshoe with very long legs and a closed top. In the middle was a low wall between the rounding pillars – metae - that ensured that the racing chariots were not taking any shortcuts. The wall – spina – was richly ornamented, and the obelisk that Augustus put there, can today be seen at Piazza del Popolo.

By the time of Julius Caesar, 1 century BC,  Circus Maximus had stone or wooden seating, senator’s boxes, a safety canal surrounding it and lots of other permanent facilities. The capacity were about 150,000 people.

Later on, Circus Maximus reached it’s maximum in 4th century AD, when Constantine had it enlarged up to 600 x 200 meters (2000 x 600 feet). A late antique reference to it mentions its capacity as being 385,000 people , but today 250,000 is believed to have been the upper limit.

The main use was horse racing with chariots, but also parades and religious celebrations were held here – ludi circenses. Mind you that Rome for political reasons had about 150 holidays in the 4th century AD, so they had good use for stadiums. Up to a dozen chariots competed in every race, and dozens and more races were held when there was an event. The chariots were two-, three- or four-in-hands, and raced for seven laps. Teams – factiones – were the whites, reds, blues and greens, but later on it was decided that only the green and blue teams could race. These teams would later on play an important political part in 6th century Constantinople.

Today nothing remain of the Circus, except for the above mentioned obelisk. The best preserved Roman circus is the one by Maxentius' palace at Via Appia.

Reference: ne, britannica