It was the largest ouvrage in the Alps[1] It is part of the fortifications surrounding Sospel, which protect the approaches to Nice from the north.

Monte Grosso, like L'Agaisen to the southeast, features gun turrets on a commanding height, at 967 meters.

Monte Grosso was built between November 1931 and June 1935, by a contractor named Borie.

[2] An additional block near the entrance with a GFM cloche and two 75mm mortars was never built.

On the 20th, it received fire from Italian 149mm guns, with a hit on its 75mm turret.