What is the X in X-mas?
1580s, from French hippodrome, from Latin hippodromos "race course," from Greek hippodromos "chariot road, race course for chariots," from hippos "horse" (see equine) + dromos "course" (see dromedary). In modern use for "circus performance place," and thus extended to "large theater for stage shows."
ancient Greek stadium designed for horse racing and especially chariot racing. Its Roman counterpart was called a circus and is best represented by the Circus Maximus (q.v.). The typical hippodrome was dug into a hillside and the excavated material used to construct an embankment for supporting seats on the opposite side. In shape the hippodrome was oblong, with one end semicircular and the other square; it thus resembled a U with a closed top. Seats ran in tiers the length of the arena and along the curve, while at the straight end dignitaries occupied seats above the arena's offices. A low wall called a spina ran most of the length of the stadium and divided the course. The spina was decorated with monuments and had sculptures that could be tilted or removed to keep spectators informed of the laps completed by the racers. Because as many as 10 chariots raced at one time, the breadth of the course was sometimes as much as 400 feet (120 m); the length was about 600 to 700 feet (180 to 210 m)