The Monastery of Mancelos, mentioned as early as 1120, represents an example of noble intervention in the creation and maintenance of private churches. Initially associated with the Portocarreiros lineage and later with the Fonsecas, the monastery was integrated into the order of the Canons Regular of Saint Augustine. The inscription dated 1166 on a church stone suggests the possibility of it being the year of the temple’s consecration or dedication. However, the remaining architectural vestiges indicate a chronology closer to the 13th century, especially visible in the main portal. This portal is protected by a galilee, explaining its good state of conservation, with elegantly sculpted capitals and a smooth tympanum supported by figures resembling atlantes. The galilee, the tower, and other elements, such as battlements, confer monumentality to the church, which underwent significant modifications in the centuries following its construction. Marks on the masonry and structural additions are evidence of these transformations. On the south side, where the cloister was presumably located, an arcosolium still guards a tomb. Inside, only the triumphal arch recalls the Romanesque construction, as the space was significantly modified due to Counter-Reformation interventions. Additionally, near the monastery, there is a cemetery where the painter Amadeo de Souza-Cardoso (1887-1918), a prominent figure of Portuguese Modernism, is buried.