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Tomen y Bala Castle Mound is a medieval motte built on bedrock of Ashgill mudstone, siltstone and sandstone in Wales. The mound rises prominently from the local landscape, a characteristic earthwork of the Norman and early medieval period designed to support a timber palisade and central tower. Its foundation rests on the weathered surface of Ashgill rocks, which provided stable ground for the substantial earthwork even as it was susceptible to erosion over the centuries.
The castle mound represents the defensive architecture typical of the twelfth and thirteenth centuries, when such structures commanded local territory and served administrative functions. The Ashgill bedrock, composed of fine-grained sedimentary deposits laid down during the Ordovician period, would have determined the mound's construction technique and structural integrity. Over time, the softer mudstone and siltstone elements weathered faster than sandstone layers, creating the worn contours visible today.
The monument is protected by Cadw under reference ME016, recognising its significance as a surviving example of motte-and-bailey castellation in the Welsh landscape. The mound's persistence on this geological foundation for nearly nine centuries demonstrates both the effectiveness of medieval engineering and the enduring character of the underlying Ashgill geology.
Tomen y Bala Castle Mound is a scheduled monument protected by Cadw under reference ME016. View the official record →
Tomen y Bala Castle Mound is a medieval motte built on bedrock of Ashgill mudstone, siltstone and sandstone in Wales. It is designated a Scheduled Ancient Monument by Cadw under reference ME016.
Tomen y Bala Castle Mound dates from the medieval period, and is classified as a motte. It is one of over 32,000 scheduled monuments protected across the UK.
Tomen y Bala Castle Mound 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 ME016.
Several scheduled monuments lie within 10 km, including Llanfor Roman Fort and Camps (revealed by Aerial Photography) (0.8 km), Castell Gronw Castle Mound (1.1 km), Pen-Ucha'r-Llan Ringwork (1.3 km).
This page is just one thread. A full Aubrey report pulls together 13 strands of Tomen y Bala Castle Mound'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.
Tomen y Bala Castle Mound stands on Ashgill Rocks (Undifferentiated), bedrock that formed in the Ashgill. The rock here is mudstone, siltstone and sandstone.