The Palio di Siena (known locally simply as Il Palio) is a horse race that is held twice each year, on July 2 and August 16, in Siena, Italy.
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.

Source: Wikipedia