The quadriga was a four-horse chariot, the most common type that was raced. There also was the two-horse biga, in which novices often competed; and less often, one drawn by three horses (triga), which tended to run only in races with religious connotations. Even more difficult to manage, and all the more impressive when they were, were chariots drawn by six (seiugae), eight (octoiugae), or even ten (decemiugae) horses. Diocles boasts of having won with six and even seven horses, a number that had never been seen before.
The Latin for a racing chariot is currus circensis, from which the word "curriculum" derives for a race or lap.
This first-century AD pottery lamp is in the Antikensammlung (Berlin). In the background, one can see the obelisk of Augustus, the dolphin lap counter, the metae, and other ornaments of the spina. The girth around the belly of the horse meets the chest girth at the withers, where both are fixed to the yoke.
Reference: The illustration is taken from Gladiators and Caesars (2000) edited by Eckart Köhne and Cornelia Ewigleben.
