According to some historians, this church was the capital of the diocese of Britonia until the second half of the 9th century, when it was replaced by Mondoñedo. The construction, which preserves vestiges of the ancient basilica and early Christian tombs, consists of three naves separated by arches supported by cruciform pillars that hold the transverse arches. The tower located at the right angle of the facade stands out. It preserves several inscriptions, the most interesting of which dates back to the 9th century and is located on the interior wall of the southern nave, making reference to the consecration of the church.