The Rocca Malatestiana (castle), built by Cardinal Albornoz (from 1380) over a pre-existing edifice which had hosted, among the others, Frederick Barbarossa and his nephew Frederick II. It was completed by the Papal governor Lorenzo Zane in 1480, and was used by Cesare Borgia as jail for Caterina Sforza. It has octagonal plant, with two main towers, the higher maschio and the lower foemina