It was built in 1280, at the time of Nicolò III, and rises on a previous Benedictine structure of the IX-XI century. Its renovation in its present form, perhaps designed by Antonio da Sangallo il Giovane, dates back to around 1536. is due to the will of Count Sforza-Marescotti and his mother-in-law Beatrice. Quadrangular in shape, it has 4 bastions, Ghibelline battlements and is surrounded by a moat; despite being austere and imposing, it has a certain elegance, typical of Renaissance dwellings. It has an Italian Garden, wanted in 1611 by Ottavia Orsini, which is considered a valuable model, because it has reached our days almost intact; divided into 12 rectangular parterres composed of mixed hedges (myrtle, laurel-ceraso, bosso, viburnum), in the center it has a peperino stone fishpond with 4 arches, surrounded by a balustrade, perhaps the work of Vignola. At the corners of the parterres there are spectacular lemon trees contained in terracotta pots.