One of the sites I follow on Facebook is a French site, "Passion Fortification". They have published some photos using a drone over Forte Centrale in the Alpes Maritime. The photos were taken by Drone de Regard.
The Italians built a number of forts on the border between Italy and France during the 1880's and 1890's. These were taken into France at the end of WWII, in 1947, I assume as part of the peace treaty between France and Italy.