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Cell of Penmon Priory on Priestholm Island, Puffin Island or Ynys Seiriol, The Monastic Settlement

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Map ReferenceSH68SE
Grid ReferenceSH6515082150
Unitary (Local) AuthorityIsle of Anglesey
Old CountyAnglesey
Type Of SitePRIORY

1. Puffin Island is a Site of Special Scientific Interest (SSSI), home to at least 10 species of seabird including Puffins, Guillemots, Razorbills, Cormorant, Kittiwakes, Herring Gulls, Great and Lesser black-backed gulls, Fulmars and shags ( There is no public landing allowed on the island without the prior permission of the landowner.

2. 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 transept. 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 transept 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 (NPRN 424033). 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.

Sources: Hughes in Archaeologia Cambrensis sixth series I (1901), 85-108
RCAHMW, 1937. An Inventory of the Ancient Monuments in Anglesey, London: HMSO, pp. 141-4, Frontispiece, Plates 185-6.
Carr, A. 'Medieval Anglesey' (1982), 287-8

RCAHMW, February 2011

New remote sensing, terrestrial and marine investigation undertaken on Puffin Island or Ynys Seiriol during 2017 (remote sensing collection and desk-based analysis) & 2018 (field survey and maritime survey) by the Royal Commission on the Ancient and Historical Monuments of Wales (‘Royal Commission’) and the Geological Survey of Ireland (GSI) as part of the EU-funded CHERISH Project, managed by the Royal Commission (Driver 2023). Two visits were made to the island for fieldwork, on 21st June 2018 for laser scanning and photographic survey of the church and telegraph station and on 26th November 2018 for an Unmanned Aerial Vehicle (UAV) or drone survey of the church. The team was very grateful to the landowner, Sir Richard Williams-Bulkeley, for granting permission to access and survey the island on both occasions.

The new surveys have generated state-of-the-art 3D records of the medieval priory church and associated structures, allowing any future adverse change to be measured to within a few millimetres. The airborne laser scanning survey of the heavily vegetated island has allowed the woodland and undergrowth to be ‘stripped away’ revealing a previously hidden archaeological landscape of ridge and furrow cultivation, field boundaries, a newly-recorded promontory enclosure and new detail of the monastic settlement. The marine survey has precisely mapped the seabed around Puffin Island providing an up to date assessment of inshore shipwrecks whilst allowing a seamless onshore/offshore 3D map to be made of Puffin Island for the first time. Both visits involved surveys of the church, reported in NPRN 424033.

T. Driver for the CHERISH Project, RCAHMW, 30/01/2023

© Crown: CHERISH PROJECT 2020. Produced with EU funds through the Ireland Wales Co-operation Programme 2014-2022.


Driver, T. 2023. Puffin Island or Ynys Seiriol: Archaeological investigation of the church, monastic settlement and wider landscape for the CHERISH Project, 2017-18. CHERISH Report No. CH-RCAHMW 10. Unpublished Report; RCAHMW.

Hughes, H. 1901. Ynys Seiriol. Archaeologia Cambrensis Vol. I. Sixth Series. 85-108

RCAHMW, 1937. An Inventory of the Ancient Monuments in Anglesey, London: HMSO

application/pdfCHR - CHERISH Project ArchiveReport entitled: 'Puffin Island / Ynys Seiriol: Archaeological investigation for the CHERISH Project, 2017-18 - Landowner’s Site Assessment - Survey legacy, climate change priorities & recommendations. Produced as part of the CHERISH project from survey work carried out June and November 2018.