The walls of Siena that we see today are the result of a long process of construction, modification and urban growth that began in the Middle Ages and ended in the mid-sixteenth century. When describing walled cities, we speak of the first circle, the second circle, up to as many as seven circles.
There is no mention of concentric buildings, but of walls added in the various historical periods. The distinctive feature of Siena compared to other cities was the uneven territory, which imposed areas with steep ascents and descents. The new circles that were built did not incorporate the previous ones. They were enlarged to absorb houses, buildings and churches, but always reconnecting with the existing layout. The stretch that we can consider the oldest of the walls of Siena dates back to the consular period and the urban need to connect small villages and fortresses. Today, these are still partially visible on the sides of Porta Camollia. From 1250, the city expanded and it was necessary to build more on the Terzo di San Martino, building the Porta di Busseto, San Viene, Fontebranda and the second Porta Romana.
The city walls had towers and started from the Porta di Busseto, reaching Porta Pispini and then the current Porta Romana, continuing to Porta Tufi, Porta San Marco and Porta Laterina. In Siena, in the fourteenth century, there were more than thirty-five entrance gates. The city was in continuous economic expansion, making it one of the most important cities in Europe. The protection and fortification of the city were very important: every Military Unit or "Societatis" was commissioned to guard one of the Gates.
With the black plague epidemic of 1348, the decrease in population was drastic, so much so that urban development was halted, incorporating only the Basilica of San Francesco which until then had remained outside the walls. The building of the walls resumed in the northern area with the conquest of the city in 1555 by Florence and the Medici family.