The Fort de Libéria, built in 1681 above the village of Villefranche-de-Conflent by Vauban, was later fortified by Napoleon III. Between 1850 and 1856, considerable works were carried out, in particular, to rectify the error of Vauban, who had it built too far back from the city. Too much of a distance allowed enemy forces to pass between the village and the fort without being detected, either from above or below. In his fear of the possible return of the Spaniards, Napoleon III had three works built, half-bastions, half-square towers, in the Mont Louis valley, Vernet-les-Bains, and Prades, which served as gun ports with crossfire. The entrance to the fort was transferred to the northeast and protected by a round tower.