Handed over centuries as the Domus Regia, the first residence of King Roger II, the Osterio Magno, from the Latin hosterium that is a fortified palace, was built in the thirteenth century by the noble family Ventimiglia del Maro, marquises of Geraci and princes of Castelbuono. Used as a winter residence, the Osterio Magno originally included other buildings and gardens, extending for a very large area that counted several facilities, different for time of construction and architectural style. In a drawing by an unknown author dating back to the sixteenth century, a shred of a larger topographical map found during the restoration work, it is possible to see the Osterio Magno with its high tower, at the corner of Corso Ruggero and Via G. Amendola, at the center of two large buildings that bordered an open space where a well is depicted. A big arch on the road connected the actual complex to the buildings in front (today seat of the tourist office) where the kitchens and the service rooms were allocated.
The palace was owned by the Ventimiglia family until 1599, when Giovanni III Ventimiglia sold it to Simone da Fiore. At the death of the latter, in 1605, the heirs gave it to the friars of the Convent of San Domenico, who granted it to several emphyteuti (the emphyteute enjoys dominion over another person’s property by paying a fee to the owner) who adapted it according to their needs in housing, stores, warehouses and even in prison. In possession of Ventimiglia was also the building called Osterio Piccolo, of which it is still possible to observe the tower, with its mullioned window, incorporated in the bell tower of the adjacent Church of Maria SS. Annunziata in Corso Ruggero. On the occasion of a restoration concluded in 1988, archaeological explorations by Prof. Amedeo Tullio have discovered, below the Osterio Magno, a residential complex of Hellenistic – Roman age and some stone artifacts, including a large jar containing bronze coins dating from the late fourth century. b.C. and a large cistern dug into the rock, now still perfectly visible in the room on the first floor of the building. Of Norman epoch are the walls at the base of the angular Tower. Several studies have tried to date more precisely the whole complex but there is no certain news about it. The most ancient nucleus is individuated in the palazzetto “bicromo”, so defined because of the architecture that characterises it, with alternating light and dark horizontal bands of tuff and lava stone, where two elegant mullioned windows are preserved, clearly visible from the outside of the building in Via G. Amendola, witnesses of the splendour of which the palace had to enjoy at the time.
A last constructive phase dates back to the elevation of the Tower, occurred in the first decades of 1300, with its development on three floors in height and a crowning with battlements to defend the building, well visible in the drawing and today no longer existing.