The most ancient part of the walls was presumably built by the Massetani in the XII-XIII century. Between the XIII and XIV century, the circuit of walls was enlarged as a consequence of the expansion of the upper town (Cittanuova). Under the Sienese domination, the walls were partly destroyed and subsequently reconstructed in 1377. The original perimeter of the walls was reduced and some parts of the city, among which the Church of San Francesco, were left outside the walls. Luckily, wide sections of the walls and almost all the gates have survived and can still be seen today. The walking tours along the outer part of the walls and between the gate of San Francesco and the Convent of the Clarisse in the Cittanova are an extremely interesting experience.