Located on the border between Tuscany and Umbria, the eerie ruins of Pierle Castle dominate the eponymous valley and the small village gathered around its walls.

The castle was first mentioned during the 10th-century and was owned by the Marquis of Monte Santa Maria Tiberina. It was strategically located at the intersection of many roads. During the 13th and 14th-centuries, the castle played a crucial role in the struggles between the Tuscan city of Cortona and the Umbrian city of Perugia.

In 1371, Francesco I from the Casali family, who was recognized as lords of Cortona and Pierle by the Florentine Republic, strengthened the castle to defend his city. This came as the tensions with Perugia rose to a climax. In 1387, 60 conspirators and rebels were savagely tortured and murdered inside the castle. In 1428, the valley acquired its economic and legal independence from Cortona and a commune was established.

The castle was partly demolished in 1576 by Grand Duke Francesco I De Medici to prevent highwaymen and enemies from seeking shelter in the building. It has been abandoned ever since, although its impressive walls measuring at over 700 feet (220 meters) in length, its towers, and massive inner keep are visible from afar.