An important example of pentagonal military architecture, the Fortress of Montalcino was built in 1361 by Mino Foresi and Domenico di Feo, partly reusing previous 13th-century structures, incorporating the keep of S. Martino, the S. Giovanni tower. The appearance is the classic one of a pentagonal castle with towers at all angles. The south-east tower is flanked by the keep. . Always a strategic and powerful ally of Siena in struggle with Florence, the castle was destroyed, occupied and rebuilt several times through centuries of bloody battles.
Around the middle of the sixteenth century it became the last bulwark of the resistance of the Sienese Republic against the Medici conquest and the external spur dates back to this period.
Some previous structures were incorporated into the fortress, such as the tower of San Giovanni, an ancient basilica that became the chapel of the castle and the keep of Santo Martini.
The castle is still completely intact today, and today the visitor can access the battlements and towers from the internal courtyard from where you can enjoy a wonderful view. The walls and towers are equipped with an external patrol walkway, still entirely practicable today.