The Mont Agel ouvrage was originally planned as a series of casemates in the eastern edge of the summit plateau, with four casemates each for 75mm and 155mm guns. An access gallery would run across the width of the plateau to an aerial tram station. The plan that was adopted and built was much more compact and could fire in all directions. The ouvrage was built by Thorrand et Cie. between November 1931 and July 1933 at a cost of 23 million francs, including the observation post. The aerial tram cost 1 million francs.