Castel del Monte and the octagon: geometry and legends of Frederick II
Eight sides, eight towers, eight rooms per floor: documented history, octagon symbolism and fanciful theories about Castel del Monte in Apulia.
On the summit of a hill in the Murge, in the territory of Andria, visible from kilometres away, rises a castle unlike any other. It has the shape of a perfect octagon, with eight towers, themselves octagonal, at the corners and an eight-sided inner courtyard. On each of its two floors eight trapezoidal rooms follow one another, connected by spiral staircases built into the towers. Castel del Monte, commissioned by the Emperor Frederick II of Swabia, has for centuries been one of the most debated monuments of the European Middle Ages.
What the documents say
The most important document is a mandate of 29 January 1240, by which Frederick ordered materials to be prepared for the castle near the church of Santa Maria del Monte. We do not know for certain whether work had just begun or was already under way at that date, nor whether the castle was ever completed in all its parts. Frederick died in 1250 and there is no evidence that he stayed there for long.
The function of the building remains uncertain. It lacks the moats and defensive structures typical of fortresses, while it has refined features such as fireplaces, systems for collecting rainwater, portals in coral breccia and marble. Many scholars interpret it as a prestige residence, perhaps linked to hunting, the emperor's passion, who wrote the treatise De arte venandi cum avibus on falconry.
The symbol of the octagon
In Christian tradition eight is the number of resurrection and new life: Christ rises on the day after the Sabbath, the eighth day. For this reason many baptisteries have an octagonal plan. The octagon is also the shape of the Palatine Chapel in Aachen, built by Charlemagne, an imperial model that Frederick knew well, having been crowned king in that city in 1215.
The octagon also stands halfway between the square, symbol of the earth, and the circle, symbol of heaven. This reading, widespread in medieval thought, makes it possible to see in the castle an image of imperial power as mediator between the earthly and the divine order. It is a plausible interpretation, consistent with Frederick's ideology, although not documented by texts of the period.
Theories and fantasies
Around Castel del Monte hypotheses of every kind have flourished: astronomical alignments with the solstice sun, the use of the golden section, links with the Templars, even the safekeeping of the Holy Grail. Some observations on its orientation deserve attention, others are suggestions without historical foundation. Frederick's court hosted astrologers such as Michael Scot and translators of Arabic texts, and this has encouraged the idea of a castle built as a secret calculation.
Inscribed on the UNESCO World Heritage List in 1996 and depicted on the Italian one-cent euro coin, Castel del Monte continues to challenge those who visit it. In the centuries after Frederick it was also used as a prison and then abandoned, stripped of its marbles, before the Italian state purchased it in 1876. Its geometry is certain, its purpose is not: it is precisely in this gap between perfect form and unknown function that the fascination surrounding it is born.