largest of the Roman hippodromes (hippodrome) and one of the largest sports arenas ever built. A U-shaped structure with seats on three sides and a low wall running down the middle of the arena around which the chariots raced, it was rebuilt in the time of Julius Caesar (1st century BC) to seat an estimated 150,000 spectators. Enlarged by later emperors, it reached a maximum size under Constantine (4th century AD) of about 2,000 by 600 feet (610 by 190 metres), with a seating capacity of possibly 250,000, greater than that of any subsequent stadium. Nothing but the site, between the Palatine and Aventine hills, remains today.