Due to many consecutive renovations, the parish church of Sant Tomàs or Sant Martín de Casarilh has not retained its original Romanesque appearance. A number of added structures have been built on – expect on the southern section – and mean that the original Romanesque place of worship is almost invisible to the visitor.

Based on a Romanesque nave, the building was extended to the north with a modern structure that became a side aisle. The semicircular apse that concludes the Romanesque nave is included in a quadrangular structure that serves as a sacristy.

The church of Saint Tomàs has a small nave, covered by a wooden vault. It too has been heavily renovated, but retains the original semi-circular Romanesque apse. A Renaissance-era baptismal font, standing on a Romanesque pedestal with a noteworthy Romanesque Christ, dates from the 12th to the 17th centuries. Nearby, there is an interesting white marble tombstone, dating from the Paleocristian period, with a handsome Chrismon. Part of the church is conserved in the Museu dera Val d’Aran.