The redoubt (1900 m) and the Roche-la-Croix battery (2100 m) were built between 1884 and 1889 on the model of General Séré de Rivières.
The whole complex, a lock on the Col de Larche, covers the Viraysse battery (2770 m) on its left flank and Fort Tournoux to the rear.
At 1900 m, a concrete structure, dug under the stone structure, was built from 1931 to 1936, as part of the Maginot Line of the Alps.
Like all "Maginot" forts, only the fighting blocks - 6 in this case - are visible, with their embrasures or armoured bells, and in particular the imposing block no. 5, the raison d'être of this artillery structure.
This unique artillery block, equipped with an eclipse turret, prevents access to the pass.
A crew of 161 men served this structure, which has retained its armament and power station.
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