Fort Libéria is a former military installation in the French commune of Villefranche-de-Conflent in the department of the Pyrénées-Orientales, at the confluence of the rivers Têt, Rotjà, and Cady.

Constructed to defend the newly acquired territory of the Roussillon following the Treaty of the Pyrenees (1659), it was designed by Louis XIV's military engineer Sébastien Le Prestre de Vauban on a hill above the village of Villefranche-de-Conflent.

It also functioned as a prison: two of the women accused in the Affair of the Poisons were locked up in the fort in 1682 by order of Louis XIV, and died there after being imprisoned for decades.

The fort, and the 734-step long underground staircase leading to it, is classified by the French state as a monument historique, and it is also listed by UNESCO as a World Heritage Site.

The fort was constructed by Sébastien Le Prestre de Vauban, the military engineer of Louis XIV, after Catalonia was divided between Spain and France following the Treaty of the Pyrenees (1659).

Vauban redesigned the fortification of Villefranche-de-Conflent and added six bastions and gate houses to it in 1679, but still considered it vulnerable, and decided to defend it with a fort on the hill called Belloch, behind the city.

These fortifications (including Mont-Louis and Fort de Bellegarde) were to block access to the Têt and Segre valleys, and were built with angular slopes to resist artillery.

[5] Initially, the fort was but poorly manned and equipped, and window coverings were installed so that the few pieces of artillery could be moved from one position to another, giving the impression of more weaponry than was actually present.

Guesdon, he noted, had managed to save up 45 French livres from her daily allotment of eight sols for food; she requested that her cellmate be given as much as she needed, and the remainder was to be used for prayer.