The church of Sant Andrèu de Casau is a perfect architectural example which clearly illustrates one of the typical characteristics of Aranese ecclesiastic heritage: the co-existence of different artistic styles in the same building. The baptismal font is a magnificent example of Romanesque iconography with a marked figurative and symbolic charge; the outside surface of the basin narrates the Christian discourse which avails itself of fish symbolism, amongst others, to address the regeneration and immortality of the soul through the sacrament of baptism.

Another Romanesque element of the church of Sant Andrèu is the sculpted Christ embedded at the top of the entrance facade.
While on the subject of the Romanesque legacy of the church of Casau, final mention must go to a wood carving of the Virgin Mary with the Child Jesus in her lap; recent restoration work has totally recovered the original polychrome work of this piece.
The rest of the religious building features elements dating from different periods. These include a Gothic access facade (15th century), the belfry, which like most of the belfries in Aran, was built during the 18th century and, above all, a magnificent sculptural ensemble including splendid examples of the religious imagery of the 17th and 18th centuries.