Founded in the 12th century by Pierre de Marsan, the city had a large fortress built around the village and a castle located on the current site of the Theatre, known as “le Castelnau”.
It was in the 14th century that Gaston III de Foix-Béarn (Fébus or Phoebus) decided to enlarge Castelnau and reinforce the Château de Nolibos, located at the northeast corner of the fortifications. It also reinforces the ramparts on the east side of the city (part of which is still visible).