The monastery on Priestholm is thought to have been an early medieval foundation. It was associated with Penmon Priory (NPRN 95543), itself an Augustinian house when it was granted to the prior and cannons of Priestholm in 1237. Following this the Prior of Priestholm shifted to Penmon. There are remains of a church, notably the twelfth century tower, and other monastic buildings, ranged within and about a walled enclosure.
The enclosure is an elongated oval, roughly 80m north-east to south-west by 36m, with several subdivisions and an inturned entrance at the south-west end. The church had a central tower, nave, chancel and south trancept. The tower rises through two stages to a low pyramidal stone roof. It has plain round headed arches. Excavations in 1896 uncovered a small early chancel, possibly pre-dating the tower which appears to bear the scar of its vaulted roof. The later chancel is thirteenth century. The trancept was overlain by a cottage, habitable in 1896.
There are traces of a complex range of buildings along the enclosure wall north-west of the church. Human bones are said to have been found in the area north-east of the church.
The monastic enclosure connects with various other boundary walls and enclosures.
Source: Hughes in Archaeologia Cambrensis sixth series I (1901), 85-108
RCAHM Aglesey Inventory 1937), 141-4
Carr 'Medieval Anglesey' (1982), 287-8
RCAHMW, February 2011