Thousands of spectators gathered in the Tuscan town of Siena for a traditional bareback horse race around the main square. The Palio di Siena has been held in the Piazza del Campo in the centre of the medieval town, twice a year, almost without fail since 1656.

Palio di Siena
Jockeys Andrea Mari of Civetta (Owl) parish and Francesco Caria of Aquila (Eagle) parish ride, during the Palio di Siena horse raceStefano Rellandini/Reuters

Siena is divided into 17 contrade, or parishes, and each enters a horse and a rider in the race, although only 10 make it to the finals. The parishes all have their own banners, jockeys' colours and mascots, dating back to the Middle Ages.

The race rarely lasts longer than a few minutes, and the winner is determined by which horse -- not which rider -- crosses the finish line first. In 2010 the horse owned by the Selva (Forest) parish crossed the line without its jockey and was declared the winner.

The winning parish is presented with the Cencio or Palio, a silk banner.

Palio di Siena
Giuseppe Zedde of Leocorno (Unicorn) parish rides his horse during the last day of practiceStefano Rellandini/Reuters
Palio di Siena
Jockeys wearing their parish colours ride their horses on the square in SienaStefano Rellandini/Reuters
Palio di Siena
An aerial view of the central square in the Tuscan town of SienaAFP
Palio di Siena
A horse named Istriceddu, from the Selva (Forest) parish, is escorted into church for a blessing ceremonyStefano Rellandini/Reuters
Palio di Siena
Supporters of the Selva (Forest) parish surround jockey Giovanni Atzeni after a blessing ceremony in a church before the PalioStefano Rellandini/Reuters
Palio di Siena
The Cencio or Palio (the banner that is awarded to the winning parish) is carried during a parade before the Palio of Siena horse raceStefano Rellandini/Reuters
Palio di Siena
A horse owned by the Leocorno (Unicorn) parish is escorted by its groom during the parade before the Palio raceStefano Rellandini/Reuters
Palio di Siena
A man wearing medieval uniform and carrying a crossbow marches into Piazza del Campo during the parish parade.Stefano Rellandini/Reuters
Palio di Siena
Jockeys ride their horses at the start of the Palio di Siena.Stefano Rellandini/Reuters
Palio di Siena
Sebastiano Murtas, jockey of Pantera (Panther) parish, crashes at the San Martino curve.Stefano Rellandini/Reuters
Palio di Siena
Carlo Sanna, the jockey of Valdimontone (Ram) parish, crashes at the San Martino curve.Stefano Rellandini/Reuters
Palio di Siena
Andrea Mari (on horse), the jockey of Civetta, or Owl parish, celebrates after winning the Palio di Siena.Stefano Rellandini/Reuters
Palio di Siena
Supporters of Civetta (Owl) parish celebrate after they won the Palio of Siena horse race.Stefano Rellandini/Reuters
palio di siena
Civetta or Owl parish supporters holds the Cencio after they won the Palio of Siena.Stefano Rellandini/Reuters