Castell Bryn Gwyn is one of a number of prehistoric sites in the fields near Brynsiencyn village. The 'castle' is a fortified enclosure, probably erected in the Neolithic period, though it appears to have been used throughout the Iron Age and the Roman period.
History
The first occupation at Bryn Gwyn appears to have been as early as 2500 BCE. Flint tools and pottery from the 3rd millennium have been found underneath the earthen walls that surround the site.
Castell Bryn Gwyn is sometimes called a hill fort, though that gives an erroneous idea of the site. It isn't a hill fort, but a defensive enclosure, built on low-lying ground. However, the shape of the enclosure and the formation of the ditch and bank defences are similar to what you might find at a hill fort.
The banks are up to 10m wide and almost 5m high in places. The entire site was originally enclosed in a second, smaller ditch, of which nothing remains.
We know little about how the site was used, but one suggestion is that it was the site of a castle built by King Olaf, ancestor of Gruffudd ap Cynan.
Getting There
Castell Bryn Gwyn can only be reached on foot via a footpath from the Caer Leb prehistoric enclosure to the east or from Bryngwym-mawr or Cefn-maesoglan to the east. A short walk away from the Castell site is Bryn Gwyn standing stones and the Neolithic Burial Chamber of Bodowyr.
There are no brown tourist signs to guide you, but there is a very brief CADW information panel on the gate that leads to the enclosure.
About Castell Bryn Gwyn
Address: Brynsiencyn,
Anglesey,
Gwynedd,
Wales
Attraction Type: Prehistoric Site
Location: On a footpath off the A4080, west of Brynsiencyn village
Website: Castell Bryn Gwyn
Cadw
Location map
OS: SH465670
Photo Credit: David Ross and Britain Express
Opening Details: Open access site, usually accessible at any reasonable time
HERITAGE
We've 'tagged' this attraction information to help you find related historic attractions and learn more about major time periods mentioned.
Historic Time Periods:
Find other attractions tagged with:
burial chamber (Historical Reference) - castle (Architecture) - hill fort (Historical Reference) - Iron Age (Architecture) - Neolithic (Architecture) - Prehistoric (Time Period) - Roman (Time Period) -
NEARBY HISTORIC ATTRACTIONS
Heritage Rated from 1- 5 (low to exceptional) on historic interest
Bryn Gwyn Standing Stones - 0.2 miles (Prehistoric Site) ![]()
Caer Leb - 0.6 miles (Prehistoric Site) ![]()
Bodowyr Burial Chamber - 0.7 miles (Prehistoric Site) ![]()
Llys Rhosyr - 2.7 miles (Historic Building) ![]()
Caernarfon Town Walls - 2.7 miles (Historic Building) ![]()
Caernarfon Castle - 2.9 miles (Castle) ![]()
Crug Farm Walled Garden - 2.9 miles (Garden) ![]()
Bryn Celli Ddu - 3.3 miles (Prehistoric Site) ![]()


