Monteriggioni is a medieval walled town, located on a natural hillock, built by the Sienese in 1214–19 as a front line in their wars against Florence, by assuming command of the Via Cassia running through the Val d’Elsa and Val Staggia to the west. he roughly circular walls, totalling a length of about 570 metres (1,870 ft) and following the natural contours of the hill, were built between 1213 and 1219. There are 14 towers on square bases set at equidistance, and two portals or gates. One gate, the Porta Fiorentina opens toward Florence to the north, and the other, the Porta Romana, faces Rome to the south. The main street within the walls connects the two gates in a roughly straight line.
The main piazza, the Piazza Roma, is dominated by a Romanesque church with a simple, plain façade. Other houses, some in the Renaissance style (once owned by local nobles, gentry and wealthy merchants) face into the piazza. Off the main piazza smaller streets give way to public gardens fronted by the other houses and small businesses of the town. In more hostile times, these gardens provided vital sustenance when enemies gathered without.