Though there are some documents dating to the end of the 12th century and beginning of the 14th century which make reference to a place called Sassofortino—distinct from the Castle of Sassoforte—analysis of the material evidence conserved in the town provide no basis for a dating earlier than the 15th century.
The City of Siena attempted to populate this area in 1339 in accordance with a group of men who had at one time lived in the Castle of Sassoforte, but met with quick failure when a terrible epidemic hit in the middle of the 14th century, creating devastation across Europe. The damage was so complete that records indicate that the two sites were definitively abandoned around 1430. The only possible trace of this first settlement is the regularity of the urban plan of the historic centre.
The architectural evidence, however, dates to no earlier than the second half of the 14th century when documents record a second agreement between the City of Siena and a group of men from Imola and Faenza.
The oldest document speaking of the castle is dated in 1076, and pertains to the donation of a small chapel and other property to the Montemassi Church, on behalf of Count Aldobrandeschi. However, over the years, the rival Ardengheschi family made several attempts to outwit the Aldobrandeschi family, who dominated most of the area in those years. They wanted to usurp power from the Aldobrandeschi’s, but instead caused problems for many. When Siena found about the problems they were causing in a neighboring town that was under its control, Siena went to war with the Ardengheschi family and conquered the Sassoforte Castle in 1328.
The Aldobrandeshci were able to retain the castle after the battle, and years later, they resold it to Siena for 5500 gold florins in 1330. The castle’s fortifications were destroyed and its inhabitants were given farmland to cultivate for the price of 600 lire. However, the inhabitants of Castle Sassoforte were soon struck by poverty and plague. Only 50 inhabitants remained in 1353. The castle passed to the ownership of the Salimbeni in 1368. In 1438, the inhabitants moved to the new residences in the Sassofortino.
The castle was abandoned for centuries. Built in rhyolite stone, it is located at the top of Mount Sassoforte. Toward the northeast, there is the quarterdeck and another structure erected near the front gate. Inside, there are doors, embrasures, a cistern, and the remains of an aristocratic abode. In front of the fortification walls, there is a rectangular structure with small, beautiful windows with vaults. The details demonstrate great care and precision, showing the great power held by the counts of Sassoforte. It might have even been the public justice building for a time. The view from Sassoforte is particularly beautiful thanks to the centuries-old chestnut groves that one encounters walking up to the mount. You can also see the sea from there. It is suggested that visits be organized in the winter and autumn months, because in the summer the thick vegetation can be perilous.