St Mary’s Collegiate Church is one of the oldest churches in the country and occupies a site devoted to religious worship since early Christian times. The building is now a National Monument. The church is likely to have been a monastic settlement of Saint Declan of Ardmore in the middle of the fifth century. It was rebuilt in Irish Romanesque style in the late eight century and the Great Nave was erected in the year 1220. Large-scale works of restoration were carried out between 1851 and 1854 possibly by W.H. Hill.
Adjoining the building is a sixty-three foot donjon tower from Norman times, which is now used as the bell tower.