"Castel del Monte is of outstanding universal value in its formal perfection and its harmonious blending of cultural elements from Northern Europe, the Muslim world and classical antiquity. It is a unique masterpiece of medieval military architecture reflecting the humanism of its founder: Frederick II of Hoenstaufen".

With these words, in 1966, the UNESCO Committee for the World Patrimony included the castle, built about 1240 by Frederick II of Hohenstaufen, in the World Heritage List.
In a letter written on the 29th of January 1240 to Riccardo di Montefuscolo, his judge and officer in Capitanata, the Sovereign ordered him to buy lime, stones, and all that would be useful and necessary "...pro castro quod apud Sanctam Mariam de Monte fieri volumus" (for the castle we want to be erected near St Mary's on the mountain). And this is the only document about the Castle we have of those times and moreover susceptible of different interpretations because of the word actractum used in it. In Latin it means pavement, or flattening out of the ground, or roof covering, till a more generic meaning of building materials.Then the only thing we have for sure is that in 1240 there were works in progress in the site, on the state of which Frederick II asked to be frequently informed. The experts don't agree on the nature of these works, if they were of foundation or of completion.

Some notes seem to strengthen the second supposition. The castle was built directly on the rocky bank and no preliminary work of levelling the ground before starting to build can be seen. It seems more reasonable that here the Latin word actractum had the meaning of "roofing" . In the Statutum de reparatione castrorum (the regulations for repairing the castles), a list of the castle structures needing repairs, written in 1241-46, Castel del Monte is mentioned moreover as a finished construction, which is justified only by bringing backwards its foundation as to 1240.
Seemingly isolated and peripherical, as a matter of fact the castle stood not far from the road connecting Andria to Garagnone, two important settlements of the period; on a hill 540 metres high on the sea level and well apparent in the distance, Castel del Monte was a fundamental component in the communication system among the defensive constructions, although great number of experts have excluded the military function of the castle as it had no moat, nor machicolations and drawbridge.

Anything but casual, and not only with respect to strategy, is the choice of the place: a hill overflowed by the sun in every hour of the day, with which the monument seems having a continuous relationship. The sunlight and the deriving shadows magnify and outline the forms of the monument, regular and yet finely different, and give value to the colours, uniform and changeable at the same time.
A relationship with the sun that in the Middle Ages conditioned the orientation of the sacred buildings and appears more than obvious in the case of Frederick II, deeply interested in astronomy and compared or even identified with our star. In this way his son Manfred announced his death: "The sun of justice has waned, the defender of peace is dead".

In Swabian world the word castrum refers to mainly defensive structures, even not excluding other kinds of exploitation; in this case the presence of baths and fireplaces on both floors of the castle, the luxurious fittings, the refined set of sculptures make reasonable to think it was used as a residence or a state residence, probably reserved to a narrow circle of privileged people, very close to the king.

It is also undeniable that owing to its high position and to its particular form Castel del Monte, still able to charm our contemporaries, excited an enormous amazement and admiration in subjects, allies, and enemies. It was, then, one of the most effective means Frederick II had imagined to impress on them the feeling of his greatness. In this respect it was the most representative product of his conception of "art serving power".
Then a plurality of functions characterized this exceptional monument, emblematic expression of the many-sided personality of its client, a man of the Middle Ages who united in himself great qualities such as a vast culture, varied interests, intelligence, tolerance, love for peace and justice to a great pride and ambition.