How did the Palio DI Siena start?

In ancient Rome, games and gladiatorial combat were quite commonplace. According to legend, the twins Romulus and Remus, suckled by a she-wolf, founded Rome. Romulus killed his twin brother, Remus; Remus' two sons, Senus and Aschius, fearing for their lives, fled north from Rome and came to an Etruscan village built on 3 hills which they eventually named after themselves (SENus and Aschius - Sena, the Latin name for Siena). They introduced to Sena Vetus (Siena) a number of so-called ludic games similar to the gladiatorial games of Rome, their natal city. Some of these games, which were actually mock battles, such as the elmora (a type of joust) and the battaglia de' sassi (a battle of hurling rocks at one's opponents) laid the foundations for the palio, a name coming from the Latin "pallium", meaning "cloth", since the prize originally consisted of a piece of valuable cloth awarded to the victorious contrada, one of the seventeen districts into which the city is divided. The name "palio" therefore refers both to the race itself as well as to the prize awarded to the winning district. These districts, or "contrade" as they are called in Italian, were at one time military companies whose main responsibilities consisted of defending the various holdings and territories of the Republic of Siena. Back in the 11th Century there were about 80 such districts. After the horrendous Black Plague of 1348 many of them disappeared or were incorporated into other districts, eventually numbering 42. In 1729 Violanta di Baviera, who ruled Siena at that time, decreed that the number of districts would be fixed at 17, which is what it remains to this day. The first references to an actual palio race, the so-called "palio alla lunga", or "straight-line palio", since it was run in a straight line, go back to the beginning of the 14th Century. In 1555 the Republic of Siena was defeated by Florentine forces with the aid of Spanish mercenaries. The military societies were disbanded but the Florentines allowed the defeated Sienese to retain the symbols and organizations of their societies, which evolved into the present-day contrade. The focus of the city then turned to within, so that the former "straight-line" palio became the "palio alla rotonda", or "palio in the round" which was raced in the Piazza del Campo, Siena's main square. This first "palio in the round" was raced in 1597 and it has continued in basically the same form up to the present day. The Palio is raced every year on July 2 and August 16 and in each race the number of participating districts is 10, with the remaining seven racing the following year. A special drawing called the "estrazione" takes place at least 30 days prior to each palio to determine which of the previous year's 10 districts will be drawn to become the 8th, 9th and 10th participants of the current year.