'U Cannuni is the castle of Mazzarino (real name not known); Military fortress of Norman origin, built around the 9th-10th century, retains a single surviving cylindrical tower and some walls. The large windows that illuminated the rooms, the fireplaces dug into the thick masonry and some rooms of the tower are still visible. It was first a military fortress, to be later transformed into the residence of the lords of the city. It was gradually abandoned as early as 1500, due to landslides that affected the area, and for the construction of the new palace of the princes of Butera, in the center of the current town.