A brief history of Offa’s Dyke

Built at the command of the eighth-century king of Mercia, Offa’s Dyke is today Britain’s longest ancient monument, following the border between England and Wales. Yet despite more than a century of study, experts still do not fully understand how or when the Dyke was built, and in recent years views have diverged even about such basic questions as its purpose

Offa's Dyke on Llanfair Hill, north of Knighton, Powys. (David Jones/PA)

Now, a new book written by two archaeologists who have been studying the Dyke for the past 15 years explores the specifically Mercian and English context for its creation. In Offa’s Dyke: Landscape & Hegemony in Eighth-Century Britain, Keith Ray and Ian Bapty explore how the Dyke may have been built and what it achieved, and consider what can be learned from it.

Here, writing for History Extra, Keith Ray explores the history of Offa’s Dyke…

What makes a simple earth ditch-and-bank dug along the frontier between Wales and England 1,200 years ago potentially fascinating to any historically-minded person living in Britain in the 21st-century?

For one thing, its length: the earthwork itself covers a distance of more than 80 miles (129km) and it ranges across a former frontier that spanned 115 miles (185km) – the latter extending from the shores of the Dee estuary in the north to Severn Estuary near Chepstow in the south. As such, this ‘great work’, built at the command of Offa of Mercia, one of the most remarkable kings to have ruled much of Anglo-Saxon England, is Britain’s (and arguably Europe’s) longest ancient earthwork.

Another remarkable thing about Offa’s Dyke is the way in which so much of it has survived: a long-distance trail, the Offa’s Dyke Path, follows much of its course, especially in the historic counties of Gloucestershire, Radnorshire, Shropshire and Montgomeryshire.

It is, however, the context of Offa’s Dyke’s building that provides most relevance to life today, because there are some remarkable similarities between events in the world of late eighth-century England and today’s Europe: warfare at the peripheries of the continent, mass-migration and, above all, Britain’s relationship with Europe were matters of considerable concern as the expansionary Kingdom of Mercia was trying to dominate all the other kingdoms and peoples of England (and especially the remaining powers of Northumbria, East Anglia, Kent and Wessex) during the reigns of Offa (757–796) and Coenwulf (796–821).

At the same time, this ‘Mercian regime’ was trying to annexe territories of the Britons of Wales and was seeking to rival the continental empire of Charlemagne, the charismatic leader of the Kingdom of the Franks, crowned by the Pope (in 800) as Holy Roman Emperor.


Silver penny of Offa, King of Mercia. 8th century. (Fitzwilliam Museum, University of Cambridge/Bridgeman Images)

The supremacy of Mercia within late eighth and early ninth-century-England was reinforced by many means, including (alongside military muscle),strategic marriage-alliances, control over the Church, assassination, new forms of taxation and new duties of military service. Among those duties was one to perform ‘bridge-work and fortress-work’, and this was probably the mechanism whereby a large work force was assembled to do the necessary aligning, quarrying, ditch-digging, soil and turf and stone mounding. This was carried out across a terrain replete with high moorland, steep-sided valleys, river-crossings and hilltops along what has become the borderland between England and Wales.

So why was the Dyke built? Firstly, it served as a deterrent: it demonstrated the might of Mercian mobilisation – any kingdom with the resources to create such a massive work could surely crush any would-be invaders. Secondly, the Dyke bolstered Mercia’s standing as a European power.

This monumental act of building also boasted clear resonances back to the works of Roman emperors. Both Offa and Coenwulf seemingly used the Dyke as a base for carrying out military expeditions right across Wales, and the way in which the Dyke traverses the landscape resonates closely with Roman frontier works – Hadrian’s Wall in particular.

Offa and Coenwulf did not see themselves as ‘kings of the English’, however, as some past Anglo-Saxon historians have suggested. They saw themselves, rather, as ‘emperors of Mercia’. The manifest destiny of the latter kingdom was, in their world-view, to absorb all the English into Mercia (and that is possibly why the Mercians sought to build no such ‘barrier’ between themselves and either Northumbria or Wessex, the compliance of both of which kingdoms in Mercian dominion was achieved in part through marriages of their kings with two of Offa’s daughters).

But how much do we really know about Offa’s Dyke? There are lots of reasons to attribute the building of the Dyke to King Offa, including a direct reference to the then 100-year-old structure by King Alfred of Wessex’s biographer, Asser (in a passage of his Life of King Alfred). However, the details of its construction are much more difficult to establish, as several archaeologists have discovered. It is still uncertain whether the Dyke was built in one go or whether its course linked up a series of pre-existing barriers built across ridge-top routes and river-valley trackways.

It is also hard to date the Dyke accurately, due to the difficulty in finding material incorporated within or under it that belongs exactly to the period of its construction. The Dyke clearly post-dates Roman period settlements, because these have been found sealed beneath it. However, turf incorporated within its bank may also pre-date it by some time, and the activities of burrowing animals over the centuries may have introduced material that considerably post-dates its creation.

At a recent excavation at Plas Offa near Chirk, for example, one radiocarbon date from turf redeposited within its bank suggested a possible origin as early as the fifth century AD, while a few metres away another sample from the base of the bank indicated a possible ninth-century date. Considerable investment of resources would be required to produce more precise dating.

What is clear from even a limited re-study of the form of the Offa’s Dyke earthwork and its positioning within the landscape is that it was a more complex construction than has previously been suggested. It builders deployed, for instance, careful scarping of natural slopes incorporated within it at several places, and careful adjustment of individual short lengths or segments along its course, to make it look bigger than it actually was. In this way the Dyke was designed to impress: not only by its huge span, but also in how it was to be seen from the west, dominating the landscape.

Besides being built to impress, the Dyke was also designed to exclude the Welsh from their former lands and was probably used as a means to raise revenue by customs control and to monitor what was going on in the area immediately to its west. Indeed, the Dyke was positioned to overlook approaches from that direction – surveillance was as important then as it is today.


Offa's Dyke on Llanfair Hill north of Knighton, Powys. (Photo by David Jones/PA)

The landscape the Dyke crossed was part of an evolving frontier that needs to be seen in the context of the development of ‘march-lands’ dividing off emergent states of the period from the surrounding peoples. This was exactly what the Franks were doing in continental Europe with the creation of the frontiers of the emergent ‘Carolingian Empire’, replete with customs-points.

The location of particularly complex stretches of the Dyke may correspond to notably sensitive ‘political places’ along the frontier where centres of Welsh power, such as may have existed on the later sites of Powis and Montgomery castles, may have been confronted by the earthwork.

This frontier, of which the Dyke formed the key – but not the only – component, may also have been made to work by creating ‘hybrid’ groups along its length. As such, mechanisms for creating and sustaining a Mercian version of what in medieval times became part of the ‘Welsh marches’ probably also included the formation of new frontier administrative units in which Welsh and English communities lived side-by-side under Mercian control.

In c895 AD Bishop Asser, with the benefit of hindsight and in the setting of Alfred’s newly-ascendant West Saxon kingdom in the late ninth-century, saw Offa’s Dyke fundamentally as a vainglorious exercise by an unscrupulous and ruthless king. While this was no doubt true (within 50 years of Coenwulf’s death the Danes had sliced Mercia in two and had all but crushed Wessex in military victories), we can alternatively see the Dyke as a measure of how ‘Mercian Britain’ could envisage a future relationship with Europe on as near-equal terms as has ever been achieved since then.

By laying down the origins of conscripted armies; economic power through trade and a regulated currency; a court culture in which queens as well as kings held sway; and the first formal ‘diplomatic missions’ (such as the one in 789 that failed to successfully negotiate an alliance between the dominant power of Europe – Francia – and Mercia), Offa’s kingdom provided a first glimpse of the role a newly-assertive Britain could play in a wider international setting. And it involved the attempt to forge a ‘new relationship’ with Europe that is arguably just as elusive today as it was all those centuries ago.

Keith Ray is the co-author (with Ian Bapty) of Offa’s Dyke: Landscape & Hegemony in Eighth-Century Britain, published by Windgather Press.

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