The Rocca Maggiore was built in 1174 as a German feudal castle. Frederick II of Swabia spent some of his childhood here under the care of Conrad of Urslingen. In 1198 the castle was destroyed by the people of Assisi and remained in ruins until 1367. The fortress was rebuilt by Cardinal Albornoz using the western section of outside walls and part of the interior fortifications. The twelve-sided tower and the long curtain wall linking the castle to the city were added by Jacopo Piccinino in 1458. In 1538, Pope Paul III built the round tower near the main gate.