Offa’s Dyke is Britain’s longest ancient monument, and one of its most impressive, yet relatively little is known about it. Thought to have been constructed along the western frontier of the Mercian Kingdom sometime in the 8th century, here are 7 facts about this remarkable earthwork.
1. It’s named for the Anglo-Saxon King Offa
The earthwork takes its name from Offa, the Anglo-Saxon King of Mercia (757-796). Offa had consolidated his power in Mercia before turning his attentions elsewhere, extending his control to Kent, Sussex and East Anglia as well as allying himself with Wessex through marriage.
Asser, the biographer of King Alfred the Great, wrote in the 9th century that a king called Offa had built a wall from sea to sea: this is the only contemporary(ish) reference we have associating Offa with the dyke. There’s no definitive other evidence that it was built by Offa, however.
2. No one knows exactly why it was built
It was originally believed to have been constructed under Offa in the 8th century as a way of marking the border between his kingdom of Mercia and the Welsh kingdom of Powys, and in doing so, excluding the Welsh from their former lands.
It was almost also certainly constructed as a deterrent, and also as a means of defense should the Welsh choose to attack. A monumental building project was also a good way of boosting standing amongst other kings and powers in England and Europe at the time: a statement of intent and illustration of power.
3. Stretches were built as early as the 5th century
The dyke’s origins have been called into doubt more recently as radiocarbon dating suggests that it actually may well have been constructed as early as the 5th century. Some have suggested that the lost wall of the Emperor Severus may well actually be the origin of Offa’s Dyke, whilst others believe it was a post-Roman project, completed by a succession of Anglo-Saxon kings.
4. It roughly marks the modern border between England and Wales
Most of the modern English-Welsh borders passes within 3 miles of the original structure of Offa’s Dyke today, showing how (relatively) unchanged it is. Much of it is still visible today, and large sections have a public right of way and are managed as footpaths today.
In total, it crosses the England-Wales border 20 times, and weaves in and out of 8 different counties.
5. It stretches a massive 82 miles
The dyke didn’t quite stretch to cover the full 149 miles between Prestatyn and Sedbury because many of the gaps were filled by natural borders, like steep slopes or rivers. Most of Offa’s Dyke consists of an earth bank and a deep quarry / ditch. Some of the earth banks stand up to 3.5 metres high and 20m wide – to construct it would have involved serious manual labour.
Much of the dyke also runs remarkably straight, suggesting that those who constructed it had a high level of technical skills. Today, Offa’s Dyke is Britain’s longest ancient monument.
6. It wasn’t ever quite a garrison
The dyke was effectively a defensive fortification, but it was never properly garrisoned.
There were, however, watchtowers built at regular intervals and it would have been manned by local groups in order to ensure its effectiveness. Part of the dyke’s construction was for surveillance.
7. Offa’s Dyke remains a site of cultural significance
There remains plenty of folklore surrounding Offa’s Dyke, and it is a site of significance as a form of ‘hard border’ between England and Wales which has sometimes been politicised as a result.
In this episode of Gone Medieval, Cat Jarman is joined by Howard Williams to explore the history of Offa’s Dyke and other ancient earthworks and walls which controlled borders, trade and population flow. Have a listen below.