


From Wikipedia:
The open site was a marketplace established before the thirteenth century on a sloping site near the meeting point of three hillside communities.... Siena may have had earlier Etruscan settlements.... It was paved in 1349 in fishbone-patterned red brick with ten lines of travertine, which divide the piazza into nine sections, ... held to be symbolic of the rule of The Nine (Noveschi) who laid out the campo and governed Siena at the height of its mediaeval splendour between 1292 and 1355. It was and remains the focal point of public life in the City. From the piazza, eleven narrow shaded streets radiate into the city.
The Duomo was built in the twelfth and thirteenth centuries.