The ruins of a tower mark the site of St Mary's Abbey. This was an early medieval monastery, reputedly founded in the fifth century, but is first mentioned in 1011 AD. In about 1200 it was reformed or refounded as a priory of Augustianian canons. Up until the dissolution this was an important pilgrimage centre for Wales.
The two stage tower is about 5.8m square internally with 1.1m wide walls, and stands up to 8.0m high. It may have stood at the angle of ranges to the south and west.

Source: RCAHMW Caernarvonshire Inventory III (1964), 17-20

John Wiles 14.02.08