Castell Bryn Gwyn
Has been described as a Possible Timber Castle (Ringwork)
There are earthwork remains
| Name | Castell Bryn Gwyn |
| Alternative Names | Castle of King Olaf; Bon y Dom |
| Historic Country | Anglesey |
| Modern Authority | Anglesey |
| 1974 Authority | Gwynedd |
| Community | Llanidan |
Castell Bryn Gwyn is a near circular earthwork enclosure defined by a massive rampart that remains up to 2.6m high, with an internal area in the region of 52-56m across. There is little trace on the ground of a ditch and early observers, misled by irregularities in the rampart, identified this as a Roman amphitheatre. Excavations in 1959-60 demonstrated that the monument had originated as a late Neolithic ritual henge enclosure or similar. It had later been adapted as a defensible circuit, presumably enclosing a settlement. This reuse probably occurred in the later Prehistoric period and its latest phase is associated with Roman pottery of the late first century AD. The primary Neolithic phase had a 5.2m wide stony bank with a 2.3m wide berm separating it from a broad flat-bottomed external ditch, 1.9m wide and up to 9.8m wide. There was at least one entrance, facing south-west. The ditch had partly silted up and the bank had weathered, when the bank was extended forward into a 9.0m wide rampart, revetted by a dry stone wall and fronted by a relatively insubstantial ditch. Finally the rampart was again extended to a width of 11m with a timber revetment and a new ditch was dug, 5.5m wide and 3.6m deep. The south-west entrance was blocked at this time and a Roman pottery sherd was recovered from the blocking. Trenching in the interior identified some features, although these could not be resolved into coherent structures and produced no dating evidence. (Coflein–John Wiles 09.08.07)
The monument consists of a near circular earthwork enclosure defined by a massive rampart that remains up to 2.6m high, with an internal area in the region of 52-56m across. There is little trace on the ground of a ditch and early observers, misled by irregularities in the rampart, identified this as a Roman amphitheatre. Excavations in 1959-60 demonstrated that the monument had originated as a late Neolithic ritual henge enclosure or similar
It had later been adapted as a defensible circuit, presumably enclosing a settlement. This reuse probably occurred in the later Prehistoric period and its latest phase is associated with Roman pottery of the late first century AD. The primary Neolithic phase had a 5.2m wide stony bank with a 2.3m wide berm separating it from a broad flat-bottomed external ditch, 1.9m wide and up to 9.8m wide. There was at least one entrance, facing south-west. The ditch had partly silted up and the bank had weathered, when the bank was extended forward into a 9.0m wide rampart, revetted by a dry stone wall and fronted by a relatively insubstantial ditch. Finally the rampart was again extended to a width of 11m with a timber revetment and a new ditch was dug, 5.5m wide and 3.6m deep. The south-west entrance was blocked at this time and a Roman pottery sherd was recovered from the blocking. The site has been associated with the castle called Bon y Dom built by Olaf in the 11th Century, although nothing has been proven. It was excavated by G J Wainwright in 1959-60. The north east section of the bank has been removed and overlain by farm buildings, and the south east section is overlain by the farm track, although traces of the bank are still visible either side of the track. (Scheduling Report)
Round enclosure of late neolithic and C1 construction, suspected of being occupied in medieval times. Hogg suggests this site as a possible location of "The 'base of the tomen' visible in the C12 of the castle built by Olaf before 1012 (or 1034). (History of Gruffydd ap Cynan)"
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 Reference | SH465670 |
| Latitude | 53.1784400939941 |
| Longitude | -4.29793977737427 |
| Eastings | 246530 |
| Northings | 367050 |
