The topography of Sion is very specific – situated in the middle of the Rhone Valley, the town is dotted with hills. They have always been occupied by men who have made them into observation points and defensive sites.
The most noteworthy fortifications in Sion stand on the twin hills of Valère and Tourbillon. On the summit of the latter, which is the highest, a castle was built in around 1300 by the bishop of Sion as his home.
Its foothills are occupied by the Majorie and Vidomnat towers. The other hill houses the fortified village surrounding the Valère Basilica.
Facing them, at the other end of the town, stands the hill of Montorge. There are also ruins here, remnants of the castle that was destroyed by fire in 1417 and has never been rebuilt.