The Trois Têtes plateau was a site considered strategic by Vauban for the defense of the town of Briançon in the Hautes-Alpes department. After its leveling, it was, therefore, equipped with the most important bastioned and armed front of the fortification system implemented in the 18th century. Its surface area is one and a half times that of the upper town. Divided into an upper and lower part, it protected the city both from attacks coming from the slopes of the Infernet mountain and the bottom of the Durance valley. The most defended part of the fort was built with an imposing bastioned front composed of two bastions and a half-moon lined with a lunette and counter guards.