The Fortress stands in the town centre and was built in 1335-1337 by the Sienese, who integrated the ancient Castello vescovile (Bishop’s Castle) of Monteregio in the fortress. The structure, designed by the architect Angiolo di Ventura, hosted the military contingent, which had to guarantee the safety of the city. The Fortress was divided into two parts by the new walls: this division made it easier for the military contingent to keep the city under control. In the middle of the fortress stands the Porta Alle Silici, a gate with a double door, which granted the access to the upper city and vice versa. The closure of this gate blocked the transit between the two parts of the city. The so-called Sienese Arch connected the fortress to the Candeliere tower, the symbol of the independence of the town. The tower and its architecture represents the supremacy of Siena.