Mont de la Source is an old Roman oppidum rising 3,051 ft (930 m) high outside of the village of Arrens-Marsous. It houses a medieval church that once stood on the pilgrimage route to Compostela. Destroyed and rebuilt over time, the church shows deep blue ceilings, typical of the end of the 17th century, which depict a starry sky. An altarpiece of the Virgin and angels by Marc Férrère (1674-1758) overlooks a statue of the Virgin on the high altar, offered by King Louis XIII in 1638. The bell tower consists of a square tower built in 1684, a date engraved on its bell with lily flower motifs.