Aber Castle - Pen-y-Mwd and Ty'n-y-Mwd llys

Has been described as a Certain Timber Castle (Motte), and also as a Certain Palace (Other)

There are earthwork remains

NameAber Castle - Pen-y-Mwd and Ty'n-y-Mwd llys
Alternative NamesAbermenai; Mwd Castle; Abergwyngregyn; Llan Boduan; Bangor
Historic CountryCaernarfonshire
Modern AuthorityGwynedd
1974 AuthorityGwynedd

A mound thought to be a medieval castle mount associated with a medieval mansion excavated at its foot (NPRN 309171). This is a sub-circular steep sided mound, roughly 36m in diameter and 6.6m high. It has a level summit about 17m by 14m. There are traces of a ditch on the south side, but no further defensive features have been identified. The mansion was excavated in the field to the south-east. It produced thirteenth and fourteenth century material and is identified as the llys or princely court recorded here through the thirteenth century. (Coflein NPRN 95692)

The llys or princely court at Aber was one of the principal residences of the princes of Gwynedd through the thirteenth century. Repairs are recorded in 1289 and 1303, following the English conquest. Remains were still visible in the early sixteenth century.Excavations in 1993 recovered the plan of a hall with crosswings at either end, associated with thirteenth and fourteenth century material. The hall was 11.2m by 8.0m internally. The site lies close by the foot of a castle mound (NPRN 95692). There are several other instances in north Wales of apparently unfortified houses associated with castle mounts, for example Castell Prysor (NPRN 308964), Crogen (NPRN 306558) and Rug (NPRN 306598). In these cases the mount can be regarded as an adjunct to the house, conferring a certain status and arguably furnishing a refuge. (Coflein NPRN 309171)

The earthen motte at Abergwyngregyn is situated on the south-western bank of the Afon Aber, where the narrow valley joins the coastal plain. The mound is nearly circular and roughly 6.7m high. The diameter at the base is 36.5m, and 16m at the top. There are no visible signs of masonry or of a bailey surrounding the earthwork, although there is some indication of a ditch on the south side. The motte has never been excavated

While there is no documentary evidence for the construction of the motte, it has been attributed to Hugh of Avranches, and Robert of Rhuddlan in the late 11th century. In the 13th century, however, Aber is recorded as one of the main residences of the princes of Gwynedd which could mean that either the existing mound was re-used, or that the Welsh princes copied the Norman motte-building tradition themselves. There is no written evidence describing the princes' site, and it has been suggested that the remains of the llys (court or regional centre) are located near the motte: recent excavations adjacent to the motte uncovered buildings which were associated with 13th century pottery. Leland, writing in the 16th century, claimed that part of the building was still standing in his time, and gave the alternative name Llan Boduan for the motte. Motte standing on level ground beside brook, and measuring 55ft in diameter and 16-18ft high. Traces of a large bailey to the east. Earthen Motte situated where Afon Aber debouches into coastal plane at 100ft OD. The mound as nearly circular 22ft high and 120ft in diameter at the base. There is some indication of a ditch on the south. There is no visible evidence of any masonry structure, nor for the presence of a Bailey. There is no documentary evidence for the date of the motte but it may have been constructed by Hugh of Avanches, Earl of Chester in the late 11th century (RCAHMW). The Pen y Mwd motte is supposed site of the Royal Welsh Palace of Arllechwedd PRN 4072. (Gwynedd Archaeological Trust HER)

Gatehouse Comments

Despite excavation there seem to be a good number of unresolved questions about this site. Was this the site of a pre-Conquest llys? Was the motte built in late C11 or C12 by a Norman conqueror or by a welsh prince? Did the welsh move the llys of the commote to the site of a Norman castle after the welsh regained control of the area (The traditional site was Hafod-y-celyn but this is a weak tradition) It is argued the ‘palace’ of Prince Llywelyn seen by Leland in the sixteenth century was Pen y Bryn although this argument would not exclude this motte as the site of the early medieval llys. However other evidence in Remfry may well suggest the Pen y Bryn site had much earlier origin as a llys which would bring into question this as the site of a llys. It should be noted there is some contention about this site and Pen y Bryn and care should be taken to consider all available evidence and opinion.

- Philip Davis

This site is a scheduled monument protected by law

Not Listed

The National Monument Record (Coflein) number(s)
County Historic Environment Record
OS Map Grid ReferenceSH656726
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  • Remfry, Paul, 2012, A Brief Report on Pen y Bryn and Aber, Gwynedd (Castle Studies Research and Publishing) p. 72-81
  • Morgan, Gerald, 2008, Castles in Wales: A Handbook (Talybont: Y Lolfa Cyf.) p. 233 (listed)
  • Davis, Paul R., 2007, Castles of the Welsh Princes (Y Lolfa) p. 67
  • Pettifer, Adrian, 2000, Welsh Castles, A Guide by Counties (Boydell Press) p. 18-9
  • Reid, Alan, 1998, Castles of Wales (John Jones Publishing) p. 25
  • Johnstone, N., 1997, 'An Investigation into the Location of the Royal Courts of 13th-Century Gwynedd' in Edwards (ed), Landscape and Settlement in Medieval Wales (Oxford) p. 63-5
  • Salter, Mike, 1997, The Castles of North Wales (Malvern) p. 49 (slight)
  • Davis, Paul R., 1988, Castles of the Welsh Princes (Swansea)
  • King, D.J.C., 1983, Castellarium Anglicanum (London: Kraus) Vol. 1 p. 32
  • Fry, P.S., 1980, Castles of the British Isles (David and Charles) p. 322
  • Renn, D.F., 1973 (2 edn.), Norman Castles of Britain (London: John Baker) p. 100
  • RCAHMW, 1956, A Survey and Inventory of the Ancient Monuments of Caernarvonshire Vol. 1: East (HMSO) p. 6 no. 10 online copy
  • Armitage, Ella, 1912, The Early Norman Castles of the British Isles (London: John Murray) p. 261 online copy
  • Lewis, Samual, 1849, A Topographical Dictionary of Wales online copy
  • Pennant, T., 1810, Tours in Wales (London) Vol. 3 p. 105



  • John Griffith Roberts, 2012, 'The archaeological dig in Abergwyngregyn 2010-2011 – a Preliminary Report' Aber Heritage Valley Partnership Newsletter No. 8 (supplement)
  • John Griffith Roberts, 2010 winter, 'A walk through royal Aber' Heritage in Wales online copy
  • Johnstone, N., 1993, Archaeology in Wales Vol. 33 p. 68-9
  • Hogg, A.H.A. and King, D.J.C., 1963, 'Early castles in Wales and the Marches: a preliminary list' Archaeologia Cambrensis Vol. 112 p. 77-124
  • Bezant-Lowe, W., 1924, Archaeologia Cambrensis Vol. 79
  • 1860, 'Bangor meeting -report' Archaeologia Cambrensis Vol. 15 p. 375 online copy

Primary Sources

  • Jones, Arthur (ed), 1910, History of Gruffydd ap Cynan (Manchester) p. 133 online copy


  • Davies, J.G., 2013, The Earth and Timber Castles of the Llŷn Peninsula in their Archaeological, Historical and Landscape Context (BA Dissertation University of Durham) p. 53-58 online copy