In 897 AD, Lubb b. Ahmad al-Qasi , Lord of the Upper March, returned from the County of Barcelona, where he had inflicted a mortal wound upon Count Guifré el Pilós. To protect himself, he set about fortifying the region and commissioned the Balaguer and Montsó Castles. In the mid 11th century, the Sudda or governor's residence was built inside the castle and lavishly decorated with plaster stucco and stunning polychrome.

Today, visitors can view the preserved vestiges of the structures and walls in the Fromós Castle Archaeological Garden. The stucco remains are on display at the La Noguera Museum.