A 13th-century castle situated on a hill at an altitude of 540 meters, in the Apulia region of southeast Italy. It was built during the 1240s by King Frederick II, who had inherited the lands from his mother Constance of Sicily.
Castel del Monte is well known for its octagonal shape. Eight octagonal towers are inserted on each of the eight corners. The wall curtains, built in the local calcareous stone, are marked by a string-course moulding. Eight windows with one light open on the lower floor, seven mullioned windows and only one three mullioned window, facing the city of Andria, on the upper one.
It was occasionally used as a hunting lodge and as a state prison. The main wall is 25 meters high and the eight bastions each 26 meters. The sides of the main octagon are 16.5 meters long and those of the octagonal towers each 3.1 meters. The castle has a diameter of 56 meters. The castle has two entrances, an unobtrusive service entrance and an ornate main entrance.
The octagonal plan is unusual in castle design. Frederick II may have been inspired to build to this shape by the Dome of the Rock in Jerusalem.