The Fort de Champillon (Swiss Armed Forces designation A365) is an artillery fort, intended to provide coverage to advanced positions in the Chablais plan at the eastern end of Lac Léman, and to support advanced positions such as the Fort de Chillon to the west and other positions to the south. The Chablais and Chillon forts were not considered part of Fortress Saint-Maurice proper, but were important advance works to delay and weaken an attacker before they reached the Saint-Maurice stopping line, or fort d'arrêt. The entire region is fortified with anti-tank barriers, permanent minefields and other barriers, while tunnels, bridges and retaining walls are mined or prepared for demolition. Construction at Champillon began in 1942, and was complete in 1944.
