The entire construction was revised by the engineer to ensure a better defence, and is made up of 3 different structures which mutually cover each other.
The town wall with its medieval towers was strengthened at the weak points and entirely crowned with a roof made from thick flagstones to protect it from enemy fire. The lower front was reinforced by a casemated grotto, the Cova Bastera, connected to the village by an underground stairway. Finally, in 1681, on the only high ground that the attacker could place cannons, Vauban built a fort, Fort Liberia, planned to hold a garrison of 96 soldiers.
Both in the quality of the building materials used and the adaptation to the existing buildings and to the terrain, the city of Villefranche-de-Conflent is a veritable masterpiece of fortification, still remarkably well-preserved today.