Castel del Monte, Frederick II's octagon of stone

On the top of a hill in the Murge, in the territory of Andria, rises a building unlike any other medieval castle. Castel del Monte has an octagonal plan, with eight towers, themselves octagonal, set at the corners, and it encloses an eight-sided inner courtyard. It was commissioned by Emperor Frederick II of Swabia, and its perfect form has prompted questions and interpretations for centuries. Since 1996 it has been on the UNESCO World Heritage List, and its image appears on the Italian one-cent euro coin.

What the documents say

The only certain document about its construction is a mandate dated 29 January 1240, sent by Frederick II while he was in Gubbio. The emperor ordered Riccardo da Montefuscolo, justiciar of Capitanata, to prepare materials for the castle he intended to build near the church of Santa Maria del Monte. The text uses the word actractus, whose precise meaning is debated: it may refer to supplies of materials or to specific finishing works, a sign that the building site might already have been under way.

We do not know for certain what the building was for. It lacks a moat, a drawbridge and storerooms suited to withstand a siege, and for this reason many historians rule out a military function. It has been seen as a hunting lodge, a ceremonial residence, a symbolic seat of imperial power. After Frederick's death in 1250 the castle had mixed fortunes: it also served as a prison for the sons of King Manfred after the Angevin victory, and in later centuries it fell into long neglect, until modern restorations.

The geometry of eight

The building is dominated by the number eight. Each of its two floors has eight trapezoidal rooms; there are eight towers and eight sides to the courtyard. In Christian symbolism eight represents resurrection and eternity, the day that follows the seven of creation: this is why baptisteries and fonts often had an octagonal plan. The octagon is also the figure that mediates between the square, symbol of the earth, and the circle, symbol of heaven, and from this point of view the castle appears as a bridge between two worlds.

The materials reinforce this impression of extreme care. The main portal, in coral breccia, recalls classical models and was probably conceived as a triumphal arch. Some rooms were faced with marble and fitted with fireplaces and sanitary facilities that were sophisticated for the time, connected to a system collecting rainwater that ran from the terraces down to the cisterns.

Esoteric readings

In the twentieth century interpretations of every kind flourished. Some scholars proposed astronomical alignments, arguing that the shadows cast by the walls at the solstices and equinoxes followed precise patterns. Others saw the castle as a temple of the Grail, an observatory, a place of initiation linked to the Templars or to the Arab culture that Frederick admired. These are evocative hypotheses, none of them confirmed by medieval sources, and they should be read as modern attempts to give voice to a documentary silence.

What is certain is that Frederick II, called «stupor mundi» by the English chronicler Matthew Paris, was a ruler curious about astronomy, mathematics and natural philosophy. The astrologer Michael Scot worked at his court, and he was in contact with the mathematician Leonardo Fibonacci. Castel del Monte reflects that culture. Whether it hides initiatory secrets or simply a lofty idea of harmony, the stone continues to speak to those who look at it.