Fortress Saint-Maurice is not a single, connected fortified position, but rather a series of mutually supporting self-sufficient fortifications that dominate of the Rhône valley between Saint-Maurice and Martigny. The Rhône in this area runs through a deep valley with the classic U-shaped glacial profile. These steep cliff walls, framing a flat valley floor averaging about wide, create a natural gauntlet. The individual forts are mined as galleries running in the valley walls overlooking the valley and each other. The higher-level forts are accessed by aerial cableways or by inclined funiculars mined within the mountains. Fortress Saint-Maurice bars an enemy moving from France into the central Alps, and to a lesser extent, prevents an enemy crossing the Great Saint Bernard Pass or the Simplon Pass from moving against Lausanne. The Saint-Maurice fortifications were supported by additional positions in advance of the main strongpoint, with major forts at Chillon and Champillon, as well as additional fortifications in side valleys and lesser thoroughfares.