Castel del Monte was constructed in the 13th century by Frederic II. It lies eighteen kilometres from Andria, near to the monastery of Santa Maria del Monte. The castle is built on one of a chain of hills in the western Murgia at 540 metres above sea level. It was listed as an Italian national monument in 1936 and added to the list of UNESCO world heritage sites in 1996. The plan of the castle is octagonal and at each external corner there is a tower, again constructed in octagonal form. The interior is divided into two floors, though it is thought that there were probably three, as the towers were five metres higher than they are now. Despite being known as a ‘castle’, the imposing building’s exact function remains a mystery. It appears not to have had a moat, though some scholars now believe that it may have had a curtain wall. It does not occupy a strategic position and it is thought that it never served as a fortress. Even the hypothesis that it was used as a hunting lodge is thrown into doubt by the absence of outbuildings or other constructions that are associated with the maintenance of animals such as horses. A final hypothesis (without any supporting evidence) is that it was intended to be a sort of temple of knowledge – a place for the undisturbed study of the sciences.