© Mapbox · © OpenStreetMap contributors · Boundary data © Cadw
Onllwyn Round Cairn is a prehistoric round cairn located in Wales and protected by Cadw under reference GM530. The monument sits on bedrock composed of Dinantian rocks—limestone formations with bands of sandstone and argillaceous material laid down during the Mississippian period, approximately 359 to 323 million years ago. This solid limestone foundation, common to the South Wales coalfield region, would have provided accessible stone for the cairn's construction and shaped how the surrounding landscape weathered and drained.
Round cairns of this type typically date to the Bronze Age, roughly 2200 to 800 BC, and served as burial monuments for individuals of status within their communities. Built by piling stones into a prominent mound, they functioned as enduring markers of territorial or ancestral significance across the Welsh uplands. The monument's survival reflects both the durability of stone construction and the relative isolation of its hillside setting.
Though undescribed in detail, Onllwyn Round Cairn remains a significant archaeological record of prehistoric burial practice in South Wales. Its protection by Cadw ensures its preservation as evidence of Bronze Age settlement patterns and funerary tradition in this distinctive limestone landscape.
Onllwyn Round Cairn is a scheduled monument protected by Cadw under reference GM530. View the official record →
Onllwyn Round Cairn is a prehistoric round cairn located in Wales and protected by Cadw under reference GM530.
Onllwyn Round Cairn dates from the prehistoric period, and is classified as a round cairn. It is one of over 32,000 scheduled monuments protected across the UK.
Onllwyn Round Cairn is a Scheduled Ancient Monument, legally protected by Cadw — the body responsible for designating and safeguarding heritage sites in Wales. The official designation reference is GM530.
Several scheduled monuments lie within 10 km, including Tramroad East of Robert's Town Bridge, Aberdare (5.5 km), Gadlys Ironworks (Remains of Blast Furnace) (6.1 km), Graig-y-Gilfach round cairn and earthwork (6.7 km).
This page is just one thread. A full Aubrey report pulls together 13 strands of Onllwyn Round Cairn's history, each drawn from the record and mapped to the exact spot:
Every location is different. Not every section appears for every place, only what the historical record actually holds turns up in a report.
Onllwyn Round Cairn stands on Dinantian Rocks (Undifferentiated), bedrock that formed in the Mississippian. The rock here is limestone with subordinate sandstone and argillaceous rocks.