For many Siena's Piazza del Campo is Europe's finest medieval public square. It is certainly one of the largest. Each year a horse race, The Palio, is run around the Piazza.
The piazza was originally a marketplace established before the thirteenth century on a sloping site near the meeting point of the three hillside communities that coalesced to form Siena: the Castellare, the San Martino and the Camollia. It was paved in 1349 in fishbone-patterned red brick with nine lines of travertine radiating from the mouth of the gavinone (the central water drain) in front of the Palazzo Pubblico
View a video of Piazza del Campo on Google Maps