Castello Borromeo was built around the year 1000 and subsequently restructured. It was Francesco Sforza in the mid-15th century who commissioned the most significant and impressive modifications designed by the architect Bartolomeo Gadio, also famous for his work on the Duomo, Castello Sforzesco and fort of Soncino. It was in this period that the imposing bastions and buttresses were built overlooking the Adda, the battlements and falconries were constructed on the walls, the irrigation channel was widened for defensive purposes, and the new section was built at the front to give the castle its present appearance. It became a military prison in 1705, and towards the end of that century was in danger of being demolished to make space for a palace for Prince Ferdinand, son of Marie Therese: but all that was lost was the main entrance gate which protected the village. In the 19th century, the castle was used as a courthouse, prison, barracks, and the right wing was used as a factory. Recent restoration work has unveiled frescoes of the Giotto school. The castle is currently in private hands and undergoing further restoration. There is a restaurant on the ground floor.p.zza Perrucchetti - Cassano d'AddaNon visitabile, se non dall'esterno.