The position and size of this stronghold of the prince-bishops made it easier to defend than the Palazzo Pretorio. Look for the evolution of architectural styles: the medieval fortifications of the Castelvecchio section (on the far left) were built in the 13th century; the fancier Renaissance Magno Palazzo section (on the far right) wasn't completed until 300 years later. Part of the Castello now houses the Museo Provinciale d'Arte, where permanent and visiting exhibits of art and archaeology hang in frescoed medieval halls or under Renaissance coffered ceilings. The 13th-century Torre dell'Aquila (Eagle's Tower) is home to the castle's artistic highlight, a 15th-century ciclo dei mesi (cycle of the months). The four-wall fresco is full of charming and detailed scenes of medieval life in both court and countryside. Reservations are required to visit the tower; check the schedule at the ticket office.