| Castell Bryn Gwyn | |
| Location: | Anglesey, Wales |
| Region: | Great Britain |
| Coordinates: | 53.1784°N -4.2978°W |
| Type: | enclosure |
| Width: | 64m |
| Height: | 1.5m |
| Material: | clay, gravel, dry stone |
| Built: | end Neolithic |
| Epochs: | Neolithic, Iron Age, Roman |
| Public Access: | Yes |
| Website: | Castell Bryngwyn Prehistoric Enclosure |
Castell Bryn Gwyn (also spelled Castell Bryngwyn) is a prehistoric site on the Isle of Anglesey, west of Brynsiencyn. It is a circular clay and gravel bank covered with grass, still some 1.5 metres (5') high and revetted externally by stone walls, which surround a level area some 54 metres (177') in diameter. Its name means "White Hill Castle".
The original use of this site is uncertain although it may have been a religious sanctuary. Later Neolithic pottery indicates use in this period, and it may have been a henge monument at this time. The earliest bank and ditch belong to the end of the neolithic period (2500-2000 BC).[1] [2]
During the Iron Age, the present wall was built, and it was rebuilt in Roman times and later.[3]
Car parking is minimal but the site is accessible from the A4080 by a footpath. Another path follows the low ridge, southwest over stiles to the Bryn Gwyn stones, or northeast, past the site of the former stone circle of Tre'r Dryw Bach, some ½ mile (800 metres) to Caer Lêb where it meets a minor road with limited car parking space.