The "Career" as it is traditionally called the race, usually held twice a year: July 2 there is the Palio of Provenzano (in honor of the Madonna di Provenzano) and 16 August the Palio of the Assumption (in honor Our Lady of the Assumption).
On the occasion of exceptional events (such as in 1969 the conquest of the Moon by Apollo 11) or the city or national anniversaries deemed relevant and appropriate (eg. The centenary of the Unification of Italy) the Sienese community may decide to make an extraordinary Palio between May and September (the last one was held in 2000, to celebrate the entry into the new millennium).
Each participating Palio Contrada only ten of the seventeen total, chosen by lot, according to a shift that is in July and August in July in August.
The mechanism is as follows:
run of the seven law Contrade not have the Palio over a year earlier;
one month before the Palio (the last Sunday in May for the Palio of July and the first Sunday after the Palio of July for the August Palio) are raffled three Contrade that will complement the batch of ten;
the other seven are extracted to determine the order of the parade and participate in the historical parade of law relevant to the Palio of the following year (retaining this order of extraction);
in case of extraordinary Palio, is a draw among all the districts to determine the ten participants.
The Palio was won by the horse, with or without a rider, after he has completed the first three laps of the square in a clockwise direction (the 'vulgate' says, "provided that the ports on the front spennacchiera, ie the rosette with the colors of the Contrada for which is running "but in reality it has only decorative value and visual aid).