Poggibonsi is a town in the province of Siena, Tuscany, central Italy. It is located on the Elsa River and is the main centre of the Valdelsa Valley.

The area around Poggibonsi was already settled in the Neolithic age, although the first traces of civilisation dates from Etruscan-Roman age, attested by a series of necropolises and by placenames such as "Talciona" or "Marturi" (from the Etruscan name of Mars).

The importance of the area dates from the 10th century, thanks to its position across the Via Francigena, the main road from Rome to France. At that time, the development of Borgo di Marte (later Marturi, Borgo Vecchio and then Poggibonsi) was started, a settlement whose origins are debated. Around 1010, Borgo di Camaldo appeared. In 1155 or 1156, the inhabitants of these and other nearby towns were moved by Guido Guerra, of the Guidi Counts, to a hill where a new settlement, Poggiobonizio, was established. In the 12th century, the Cathars had a major theological school in Poggibonsi. Declared an Imperial City by emperor Frederick II, according to Giovanni Villani it was one of the most beautiful cities in Italy. Poggiobonizio, which adhered to the Ghibellines, was destroyed by the Florentine Guelphs in 1270. After 1293, Poggibonsi remained under Florentine rule. Emperor Henry VII ordered reconstruction in 1313 as Monte Imperiale, but the work did not survive him. In 1484, Lorenzo de' Medici had a new settlement built in Poggiobonizio according to the Renaissance idea of the "Ideal City", protected by a fortress designed by Antonio and Giuliano da Sangallo. Work, however, was halted in 1510.

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