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Caer Gybi, Holyhead

Also known as, or recorded in historical documents as;

In the community of Holyhead.
In the historic county of Anglesey.
Modern authority of Anglesey.
Preserved county of Gwynedd.

OS Map Grid Reference: SH24728262
Latitude 53.31165° Longitude -4.63200°

Caer Gybi, Holyhead has been described as a Masonry Castle although is doubtful that it was such, and also as a probable Fortified Ecclesiastical site.

There are major building remains.

This site is a scheduled monument protected by law.
This is a Grade 1 listed building protected by law*.


This site has been considered by some writers to be a castle but is rejected as such by Hogg and King. The late C3 Roman fort, built to defended against Irish raiders, is alleged to have been repaired and occupied during the Middle Ages as a castle (Hughes). The site was probably occupied by a monastery from the C6 and a C13 church now sits in the site. Certainly this small (75m by 45m) rectangular fort would have provided good defence for the monastery and later church from the Irish pirates that continued to affected Anglesey.

Caer Gybi is a stoutly walled rectangular enclosure that crowned a low cliff overlooking Holyhead harbour. It is thought to be a late Roman (third or fourth century AD) strongpoint presumably concerned with maritime activities. At some point in the medieval period a monastery was established within the walls and this later became a large collegiate church (NPRN 27500). There is also a second medieval church or chapel, Eglwys-y-Bedd (NPRN 43590). In 1646 the Fort of Holyhead held a Parliamentary garrison. This is a near rectangular enclosure, about 67m north-north-east to south-south-west by 44m. The walls are 1.8m thick and rise from 2.6m (internally) to 4.0m (externally) to a wall walk and ruined parapet. The eastern side is now marked by a more recent wall along the top of the old cliff. There are round towers at each corner. Those at the western angles are about 5.0m across and appear to be original. The eastern towers are about 7.5m across. The north-east tower is thought to be a medieval rebuild, restored in the seventeenth century and late nineteenth century. The south-east tower was rebuilt in the late nineteenth century. The modern twin arched gateway in the south wall occupies an original entrance. Excavations beyond the north walls uncovered the wall of a building abutting the north-west tower. This was of similar construction to the tower and is likely to have been Roman. There was no trace of a ditch on this side. Given that the work was refortified in the medieval period, the placement of a garrison here in the seventeenth century could reflect an earlier practice. (Cofein–John Wiles 13.07.07)

Between Stanley Street and Victoria Road enclosing St Gybi’s Church, and Capel-y-Bedd, entered by gateway from Market Square. History: Late Roman small coastguard fort. Probably originally consisted of rectangular enclosure with tower at each corner, and, at lower level to E, flanking walls perhaps to quay. Former Roman E wall rebuilt in Medieval period, and again in C19, when lower churchyard was created. Some rebuilding of upper part of NE tower (itself medieval rebuild), possible C17. SE tower rebuilt C19. Description: Enclosure approximately 75m (N-S) by 45m (E-W). Wall approximately 4m high and 1.7m thick built of rubble with dressed facing stones, sometimes set in herring-bone fashion, with occasional levelling courses on inner face; 2 rows of putlog holes, lower close to ground level, and upper approximately 1.5m above. Parts of wall, especially to N survive to wall-walk level, with parapet up to 1m high. Towers approximately 5m in diameter. SE tower rebuilt on Roman foundations, and now forms part of Stanley House, as does part of S wall. South gateway of 2 arches follows original plan but rebuilt. Part of S wall incorporated into rear of No 1 Market Square. SW tower largely incorporated into C19 buildings. Parts of W wall built into tower of Church. NW tower exists partly to wall-walk level. Gateway in N wall later insertion with brick-lined arch. NE tower stands approximately 8m high from rock foundations in lower churchyard, and has, to E, bonding stones for former wall flanking quay. E wall (circa 1m thick) mainly modern. Stone stairs down to lower churchyard (which was created in early C19). Scheduled Ancient Monument: A 31. Listed Grade I as outstanding structure from late Roman period. Group value with Parish Church and Capel y Bedd. (Listed Building Report)
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Sources of information, references and further reading
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This record last updated 20/04/2017 04:03:38