The earliest known antecedents of the race are medieval.
The town's central piazza was the site of public games, largely combative: pugna, a sort of many-sided boxing match or brawl; jousting; and in the 16th century, bullfights.
Public races organized by the contrade were popular from the 14th century on; called palii alla lunga, they were run across the whole city.
When the Gran Duke of Tuscany outlawed bullfighting in 1590, the contrade took to organizing races in the Piazza del Campo. The first such races were on buffalo-back and called bufalate; asinate, races on donkey-back, later took their place, while horse racing continued elsewhere.
The first modern Palio (called palio alla tonda to distinguish it from the earlier palii alla lunga) took place in 1656.
Today, the Palio di Siena is held twice each year, on July 2 and August 16. Ten horses and riders, bareback and dressed in the appropriate colours, represent ten of the seventeen contrade, or city wards. The Palio held on July 2 is named Palio di Provenzano, in honour of the Madonna of Provenzano, who has a church in Siena. The Palio held on August 16 is named Palio dell'Assunta, in honour of the Assumption of Mary.
A pageant, the Corteo Storico, precedes the race, which attracts visitors and spectators from around the world.
The race itself, in which the jockeys ride bareback, circles the Piazza del Campo, on which a thick layer of dirt has been laid, three times and usually lasts no more than 90 seconds. It is common for a few of the jockeys to be thrown off their horses while making the treacherous turns in the piazza, and indeed, it is usual to see unmounted horses finishing the race without their jockeys.