Erected between 1053 and 1073 in Calameda, it was the diocesan cathedral of Bosa from the XV century onwards, when the episcopal seat was moved to the church of Santa Maria in Bosa. Despite the restoration work completed in 1938 having altered the original appearance, the building is one of the oldest and most interesting examples of Romanesque architecture in Sardinia.
The facade is the result of it being reconstructed in the XIII century and has three large, pointed arches. The portal takes up the central arch and is dominated by a limestone architrave, decorated with depictions of the saints Peter and Paul on its external sides, and the Madonna with Child and the haloed Emperor Costantino in the centre.
The inside has three naves and concludes to the east with the apse. The central nave, which preserves the single traces of the original XI-century layout, has a wooden ceiling, while the two side ones are cross vaulted.
An important inscription, engraved on a pilaster in the apse, records when the first stone was laid with a ceremony celebrated by the bishop Costantino de Castra, midway through the year 1000.
