The fortress, built in 1361 atop the highest point of the town, was designed with a pentagonal layout by the Sienese architects Mino Foresi and Domenico di Feo. The fortress incorporates some of the pre-existing southern walls, the pre-existing structures including the keep of Santo Martini, the San Giovanni tower and an ancient basilica which now serves as the fortress chapel. Though the town itself was eventually conquered, the fortress itself never submitted, an admirable feat, considering the size of the Sienese and Florentine forces that besieged Montalcino at varying intervals.