Castel del Monte, Apulia

Castel del Monte (Italian for "Castle of the Mountain"; Barese: Castìdde du Monte) is a 13th-century citadel and castle situated on a hill in Andria 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. In the 18th century, the castle's interior marbles and remaining furnishings were removed. It has neither a moat nor a drawbridge and some considered it never to have been intended as a defensive fortress. However, archaeological work has suggested that it originally had a curtain wall.

The castle is famous for its bold octagonal plan, and classicizing details of the architecture. In 1996, Castel del Monte was named a World Heritage Site by UNESCO, which described it as "a unique masterpiece of medieval military architecture". Described by the Enciclopedia Italiana as "the most fascinating castle built by Frederick II", it also appears on the Italian version of the one cent Euro coin.

Castel del Monte is situated on a small hill close to the monastery of Santa Maria del Monte, at an altitude of 540 metres (1,770 ft). When the castle was built, the region was famously fertile with a plentiful supply of water and lush vegetation. It lies in the comune of Andria, province of Barletta-Andria-Trani, occupying the site of an earlier fortress of which no structural remains exist.

A document dating to 1240, in which Frederick II ordered the governor of Capitanata to finish some works in the castle. It was never finished and there is no proof that he used it as a hunting lodge as commonly thought. It was later turned into a prison, used as a refuge during a plague, and finally fell into disrepair. It originally had marble walls and columns, but all were stripped by vandals or reused in constructions nearby.

Because of its relatively small size, it was once considered to be no more than a "hunting lodge", but scholars now believe it originally had a curtain wall and did serve as a citadel. Frederick II was responsible for the construction of many castles in Apulia, but Castel del Monte's geometric design was unique. The fortress is an octagonal prism with an octagonal tower at each corner. The towers were originally some 5 m (16 ft) higher than now, and they should perhaps include a third floor.

Both floors have eight rooms, and an eight-sided courtyard occupies the castle's centre. Each of the main rooms has vaulted ceilings. Three of the corner towers contain staircases. The castle has two entrances, an unobtrusive service entrance and an ornate main entrance. Frederick II's main entrance featured elements from classical architecture such a pediment supported by rather thin fluted pilasters, and may have been influenced by Frederick II's interest in Greco-Roman architecture.

The octagonal plan is unusual in castle design. Historians have debated the purpose of the building and it has been suggested that it was intended as a hunting lodge. Another theory is that the octagon is an intermediate symbol between a square (representing the earth) and a circle (representing the sky). Frederick II may have been inspired to build to this shape by either the Dome of the Rock in Jerusalem, which he had seen during the Sixth Crusade, or by the Palatine Chapel of Aachen Cathedral.

Occasionally used as a hunting lodge under Manfred of Sicily, the castle became a state prison under the latter's victor, Charles I of Anjou: here Manfred's sons Henry, Azzo and Enzo were kept as prisoner after 1266, as well as other Hohenstaufen supporters.