Castello di Monte Sant'Angelo, Medieval castle in Monte Sant'Angelo, Italy

Castello di Monte Sant'Angelo stands on the highest part of the town, built of rough light-grey and beige limestone. A tall irregular wall on the left holds a rounded archway and a stepped stone stairway with a thin metal handrail; on the right a large round-headed archway with a gridded window faces a small terrace with a metal-railed parapet. Inside, a 21-metre-long vestibule leads to a courtyard flanked by two cylindrical towers.

Bishop Orso I of Benevento and Siponto had a Byzantine castrum built here in 837–838, the origin of the castellum de Monte Gargano. In the 11th century Robert Guiscard rebuilt the oldest part, the pentagonal Torre dei Giganti, 18 m high with 3 m thick walls. Frederick II gave the castle to his bride Isabella of England, and the Angevins used it as a state prison. Francesco di Giorgio Martini modernised it for firearms between 1491 and 1497.

The name recalls the Honor Montis Sancti Angeli, the lordship held by Rainulf Drengot and later Robert Guiscard. Frederick II gave the castle to his third wife, Isabella of England, called "Isabella with the beautiful face"; the 13th-century Sala del Tesoro, with its central pillar and pointed vaults, survives from that period.

The castle stands at the highest point of Monte Sant'Angelo. Visitors enter through a portal reached by a fixed two-arch bridge over the former moat; inside, a guard post sits on the right and the stables and ammunition store occupy a large room. Two doors on the left lead outside or up a stair to the Torrione a carena. A 21-metre-long vestibule opens into the inner courtyard between two cylindrical towers.

The castle's cellars beneath the Torre dei Giganti held a prison; Philippa of Antioch, wife of the rebel Manfredi Maletta, died there in 1273. Joanna I of Naples was also confined here, and her remains are said to lie in the church of San Francesco in the town.