 Protected by the Adda on two sides, it had a high square tower on the third one.Its fortified bridge (see Trezzo sull'Adda Bridge) was long, the longest bridge span for several centuries, built on three different levels, passing over the waters.Due to its strategic position, the castle was contested first by Emperor Frederick Barbarossa and Milan, in the 12th century, and later by the Visconti and the Torriani families.