Ouvrage Du Janus
Given the existing facilities and the site's strategic importance, the site was selected for a Maginot ouvrage in 1926. Work began in 1931, abandoning some of the older work and creating new underground facilities to the Maginot Line standard. A gallery connected the new position to the Séré de Rivières works. Work stopped in July 1935 as a result of the Stresa Front agreement with Italy, but restarted in 1938 as relations with Italy and Germany deteriorated. The cost of the new work amounted to 10.3 million francs (not including armament). When the position was occupied in 1938, numerous deficiencies in heat, ventilation and optical sighting equipment were uncovered.
The Maginot ouvrage incorporates subterranean elements of the old fort, particularly the entry and underground barracks. New galleries were extended to the ends of the rock fin to Blocks 4, 5, 6 and 7 on the north and blocks 1 and 2 on the south. The massive Block 8 inherited from the original fort occupies the center of the ridge, facing southeast.
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