Ouvrage Saint-Antoine is a work (gros ouvrage) of the Maginot Line's Alpine extension, the Alpine Line. The ouvrage consists of one entry block, one infantry block and one artillery block overlooking Modane on the way to the Col du Mont Cenis. Ouvrage Saint-Gobain is just to the north, across the mountain valley. Saint-Antoine overlooks the approaches to the Fréjus Rail Tunnel and was part of an ensemble of forts, including Saint-Gobain, Ouvrage Sapey and Fort du Replaton that guarded the French end of the tunnel and the descent from the Mont Cenis pass.