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Offa's Dyke: Section from Rhydwen-Fach to Coed Pen-y-Gelli is an early medieval linear earthwork that forms part of the most substantial boundary monument in Britain. Constructed during the late 8th century, the dyke served as a frontier demarcation between the Anglo-Saxon kingdom of Mercia and the Welsh kingdoms to the west. This section runs across terrain underlain by Dinantian limestone with interbedded sandstone and argillaceous rocks, geology that would have presented significant engineering challenges to its builders.
The visible earthwork comprises a substantial bank and ditch aligned north–south across the landscape. The limestone bedrock, whilst harder than softer sediments, would have required considerable effort to excavate, and the builders exploited the natural topography to maximise defensive potential. The mix of rock types present would have yielded material of variable workability, influencing how labour was deployed along different sections of the dyke.
This section is protected by Cadw, the Welsh heritage organisation, as a scheduled monument of national importance. The earthwork survives as a prominent landscape feature, preserving evidence of early medieval territorial organisation and construction techniques. Its survival across difficult terrain demonstrates both the strategic importance of this boundary and the substantial resources invested in its creation.
Offa's Dyke: Section from Rhydwen-Fach to Coed Pen-y-Gelli is a scheduled monument protected by Cadw under reference FL109. View the official record →
Offa's Dyke: Section from Rhydwen-Fach to Coed Pen-y-Gelli is an early medieval linear earthwork that forms part of the most substantial boundary monument in Britain. It is designated a Scheduled Ancient Monument by Cadw under reference FL109.
Offa's Dyke: Section from Rhydwen-Fach to Coed Pen-y-Gelli dates from the early medieval period, and is classified as a linear earthwork. It is one of over 32,000 scheduled monuments protected across the UK.
Offa's Dyke: Section from Rhydwen-Fach to Coed Pen-y-Gelli 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 FL109.
Several scheduled monuments lie within 10 km, including Bron Fadog Enclosure (4.5 km), Round Barrow 135m SE of Lodge Farm (5.4 km), Round Barrow 225m SE of Parc y Prysau (6.4 km).
This page is just one thread. A full Aubrey report pulls together 13 strands of Offa's Dyke: Section from Rhydwen-Fach to Coed Pen-y-Gelli'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.
Offa's Dyke: Section from Rhydwen-Fach to Coed Pen-y-Gelli stands on Dinantian Rocks (Undifferentiated), bedrock that formed in the Mississippian. The rock here is limestone with subordinate sandstone and argillaceous rocks.