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Devil’s Dyke – What was it for?

The Dyke was constructed in the 5th or 6th centuries – perhaps by the Saxon kings of the East Angles in order to defend their newly established lands from attack by the Britons. It would certainly have helped provide control over the movement of people through this important communications corridor. Perhaps traders could pass over or through the wall upon payment of tolls.

Who Built the Defensive Dykes?

Who built these stop lines is a question for which there is no simple answer. It is likely that people from the delimited estate constructed the smaller dykes that were boundary markers (like Aelfrith’s Dyke and Bica’s Dyke), probably under the direction of the estate owner, but it is far less certain who ordered the construction of those earthworks that had a military purpose. It is not just that we do not know their names; we do not know what type of people built them or at least ordered them to be constructed. The actual workers could have been local farmers sick of being raided, paid workers following the orders of a king, conscripted labourers, or slaves under the control of a warlord.

It is tempting to link dykes with the rise of kings and certain kingdoms. It is fairly certain Offa ordered the construction of the earthwork that bears his name and equally Aelfrith, Bica, Lawa and Eliseg (if Clawdd Lesg is named after him) may have ordered the building of earthworks to which their names are attached. Without precise techniques for dating dykes, attempts to connect other dykes with individual kings are foolhardy. Geographical location suggests that a Mercian king possibly ordered the building of Wat’s Dyke, an East Anglian king those in Cambridgeshire and a king of Wessex possibly ordered Wansdyke, but connecting other dykes with kingdoms, let alone individual kings, is highly speculative.

It is possible that the earthworks can tell us where shadowy lost kingdoms were once located and scholars have linked dykes like the Swaledale Dykes, Tor Dike in Yorkshire and the Giant’s Hedge in Cornwall with suspected lost British kingdoms. Unfortunately, these theories usually assume that a later administrative region was once a kingdom, then fit that hypothetical realm to a nearby, possibly unrelated, earthwork. The larger dykes certainly looked planned by an authority with wide-ranging powers (as we have noted, the larger dykes were more likely to have marker banks, ankle-breakers and revetments), but most early medieval dykes are small, simple structures built by 100 men in a single season. The vague descriptive names of many dykes, as well as the supernatural monikers, all suggest that the original builders were soon forgotten; the ‘rough dyke’ names of some confirm the idea they were hurriedly built. Perhaps kings did not order the construction of the majority of the earthworks and it is likely that small agricultural communities built them to defend themselves against the predatory warlords whose descendants probably became kings. The analysis in this book of the size of labour force needed to build these dykes suggests that most were not the grandiose gestures of a king.

As Paolo Squatriti has rightly pointed out, dykes are exercises in earth moving, that is, they were a typical farmer’s solution to a problem, as peasants were always digging the earth, for example for drainage, to get at root crops, to make hedgerows to control cattle, to terrace land for ploughing, to remove tree stumps, to dig out large stones, or to bury the dead. Digging the earth was probably not the natural action of an early medieval war leader. We can only ponder what the role of women was in the growth of dykes. They seem to be excluded from active roles in warfare, except as a victim who was robbed, murdered, raped or abducted into slavery. Perhaps they encouraged men to build the dykes to protect their communities and even worked on them, helping to move the earth themselves. Their male relatives may have even been inspired to build them to protect women in their communities, or alternatively went on raids to capture females. It has been suggested that women kept alive feuds and vendettas with songs and stories; if they were primarily victims it is perhaps unsurprising that they might want to remind others of wrongs suffered by their group in the hope that compensation or at least retribution would be sought.

Evidence for Beacons

When raiding was a problem in the early medieval period people often built beacons to warn of attack. We know the Vikings and their enemies used systems of beacons to warn of the arrival of raiders and the Romans used scouts (exploratores and areani) to warn of attack. If dykes were not manned (though they may have been patrolled) as archaeology suggests, there must have been a signalling system to alert people to danger so that they could assemble at the dyke. Can we find signs of beacon sites in the period ad400–850? Can we find evidence for a prominent location with good lines of sight at a reasonable number of early medieval dykes?

Hill postulated that beacons were used both to lay out Offa’s Dyke and Wat’s Dyke as well as to warn of Welsh raiders, but attempts to locate them through excavation have proved fruitless. No charcoal deposits have been found on the top of hills he thought to be signal points. As these dykes are very long, Hill could easily have selected the wrong location to excavate and if a warning beacon was never set alight there would be little evidence of it in the archaeological record. A substantial watch tower, especially if the foundations were sunk into the ground, would leave archaeological evidence, but more flimsy structures could leave no trace. A roving scout using flags or a horn would certainly leave no evidence. If the fires from burning barns gave abundant evidence of a raid in progress, perhaps beacon fires were not needed (obviously, if the raid occurred at night it would be these fires that warned people of attack and flags would be useless). Even so, we should find a prominent hill or similar landmark near every dyke that gives good views towards the area the earthwork faced if they were designed to combat raids and a warning was needed to gather defenders.

Development near some dykes, like Faeseten Dyke in Kent, makes it impossible to tell if there are any good candidates for a nearby signal point, while at Heronbridge and some of the East Anglian dykes the flat landscape means there are unsurprisingly no obvious candidates we can identify. Significantly, at most other dykes there are obvious sites for possible beacon sites or signal points. Despite housing developments (and forestry on Ockham Common) obscuring much of Fullinga Dyke in Surrey, St George’s Hill near the north end gives good views, while the hill on which a semaphore tower was built in 1822 at Ockham Common just to the east of the dyke (at TQ089585) is a clear candidate for a signal point. This is assuming that Fullinga Dyke was more than just a border marker, however. Bolster Bank in Cornwall defines a peninsula dominated by a hill tellingly called St Agnes Beacon (at SW710504), which affords superb views across the Bristol Channel and inland. While lines of sight from Tor Dike in Yorkshire down the steep valley to the south are obscured, the high hills that flank the valley on either side would make excellent signal points. An observer on the Swaledale Dykes cannot see anyone approaching from the east until they are quite close, but people on the adjacent hills can. Similarly, the views northwards from Grey Ditch in Derbyshire are rather poor, but Lose Hill (SK153853), 2.5 miles (4km) to the north, commands spectacular panoramic views over a vast area and the hill of Crungoed (SO185711) to the north of Pen y Clawdd dyke in Powys is an excellent candidate for a signal station.

To the north of the dykes in south Wales are the Brecon Beacons, which are so named because of the fires erected on them to warn of English raiders. An observer stationed on the hills near Black Dyke and the Bardon’s Mill dykes in Northumberland (like Catton Beacon at NY822592 and Bell Crags at NY772729 where there is actually a fire watch tower today) could have given warning of imminent attack. At Lanreath, near the middle of the Giant’s Hedge in Cornwall, a bulge in the course of the dyke encompasses a hill that gives superb prospects to the north. Today, the River Severn forms a rather formidable barrier across a gap in Offa’s Dyke between Rhos and Buttington, but before modern flood defences rivers meandered across their floodplains, so it would have been much easier to ford. There are two large hills on the eastern side (Breidden Hill at SJ295144 and Middleton Hill at SJ305133), which give commanding views, so a few watchmen with a beacon fire stationed on the hills could easily warn of any attempt to ford the river by raiders.

For some dykes the evidence is less circumstantial. The views forward from some sections of East and West Wansdyke are hardly panoramic, but the two hill forts incorporated into West Wansdyke (Maes Knoll and Stantonbury), or the Downs just to the north of East Wansdyke (Barbury Hill at SU156761 or Cherhill at SU048694 in particular) overlook large areas. There is evidence of beacon sites across Wessex used to warn of Viking raids (Elizabethans reused many of the sites for Armada beacons), which may have originated in warning systems related to early medieval dykes. To the north of Wansdyke, the late Saxon fort on Silbury Hill or even the burh at Avebury could have replaced an older early-warning system for people living near East Wansdyke. They could give advance warning of attackers approaching from the north and then hopefully the locals would have a chance to man the dyke.

The hill of Glastonbury Tor overlooks Ponter’s Ball and evidence for early medieval occupation at the site possibly suggests that it was a signal point. Hills obscure the views to the south of the nearby New Ditch, but 1.2 miles (2km) west of that earthwork is the Iron-Age hill fort of Dundon Hill, in the south-east corner of which is a mound called Dundon Beacon that overlays the Iron-Age ramparts. It may be a windmill mound (though that would be better placed on the western side of the hill to face the prevailing winds), or an aborted attempt to build a motte and bailey castle, but the name suggests that the mound was built as a beacon, perhaps working in conjunction with the earthwork. Dundon Beacon overlooks land to the south of the dyke so if watchmen were stationed there and at Glastonbury Tor, it would be almost impossible to cross the area unobserved. Near Bar Dyke and Broomhead Dyke in Yorkshire are two hills surmounted by what are assumed to be Norman fortifications (Bailey Hill at SK312726 and Castle Hill at SK271923), but both could be possible older beacon sites.

As briefly mentioned earlier, along the coast to the north of Dane’s Dyke was a line of at least five signal stations, which were probably the last Roman military structures built in Britain. While today many of these sites are no longer inter-visible, they were built on cliff tops subject to erosion, so it is likely that sites that would have connected the chain have long since fallen into the sea. There is evidence of post-Roman occupation at the Filey station and excavations at the Goldsborough signal station found bodies of people who seemed to have died violent deaths dating to just after the end of Roman rule in Britain. Flamborough Head itself would have been an ideal site for a signal station, as later use of the headland clearly shows. Three beacons were erected there in 1588, while in 1674 a lighthouse (the first post-Roman British lighthouse) was built at Flamborough and in 1796 a flag station was built there. While there is no surviving evidence of a Roman or early medieval signal station at Flamborough, quarrying and erosion could have destroyed such evidence. Nevertheless, the Roman signal stations to the north could easily have given early medieval people enough warning of seaborne raiders (Picts or Angles), so that they could gather behind the safety of the earthwork.

This topographical, archaeological and place-name evidence from so many dykes, though not conclusive, certainly suggests people were using hills (sometimes even artificially heightening them) to watch for enemy attacks. We do not know if beacon fires, flags or perhaps mounted messengers (or a combination) were used, but warnings were probably sent to locals. They could then man the earthworks that blocked routeways where they hoped to see off attackers. It is just unfortunate that we do not have the written sources to tell us how many times the earthworks were effective in preventing plunder-greedy warriors raiding their victims.


Though it would be highly speculative to try to match specific dykes to individual entries in Anglo-Saxon or Welsh chronicles, we can suggest how raiding and counter-raiding measures fitted into processes like the Anglo-Saxon conquest or the rise of kingdoms. Laycock has suggested that dykes are a symptom of the breakdown of Roman rule across Britain and its Balkanization into small British and Anglo-Saxon kingdoms. It could be that it was incessant raiding that caused this fragmentation of the Roman diocese of Britain.

Raiding and the coming together of people to build dykes to combat raids could respectively destroy and build new identities; dykes could have been crucial in the formation of kingdoms and raiding. If a raid led to the ambush and murder of a king, it would lead to a kingdom’s destruction. Booty from raids may have helped warlords to become established kings and the concentration of dykes around the border of Mercia could mark a reaction to the growth of that kingdom. Those earthworks around the heartland of Powys may have helped to maintain the power of their kings. The dykes that subdivided East Anglia (like Launditch and Bichamditch) suggest that region was once disunited, though the later written sources give us no hint of that division. The very act of building, maintaining and occasionally fighting at the Cambridgeshire Dykes, probably against Mercia, may have helped to create cohesion amongst those divided communities, which eventually led to the growth of the East Anglian kingdom. The building of the earthworks on the western border of Kent may have helped to reinforce the power of Kentish kings. As already discussed, the act of building and using dykes in Cornwall to counter West Saxon raids probably helped to unite the Cornish and maintain their identity in the face of growing Anglicization. Once kingdoms coalesced and kings gained control of large areas, they would probably try to stop localized raiding (the law codes certainly suggest an attempt to replace reciprocal violence with fines) and the rulers would try to focus energies against external threats. The incessant raids of the immediate post-Roman period may have died down by the ninth century, possibly thanks to the dykes, though they were soon replaced by the incursions of the Vikings. We should note that kingdoms could also form without any need to build dykes, such as the Scottish kingdom of Argyll, as well as the East Saxon and South Saxon kingdoms.

The theory that the fifth to ninth centuries consisted of widespread raiding complements the various theories about the nature of the Anglo-Saxon settlement of England (the Adventus Saxonum) and possibly also the Scottish takeover of Pictish territory. Broadly speaking, these movements have variously been characterized as mass invasions, coups by a small group of invading warriors and cultural changes that involved the movement of very few people. Let’s look at these theories in turn.

If the Anglo-Saxon invasion involved the replacement of the native population with Germanic incomers, aggressive raiding would help to explain how they could drive out the far more numerous indigenous population. The same logic could be applied to the Scottish takeover of the lands of the Picts. In recent years, such invasionist theories have been less fashionable and the Anglo-Saxon takeover of lowland Britain has often been characterized as a coup by some Germanic warriors. The arrival of a small class of hardened Germanic fighters that had a culture of aggressive and persistent raiding is consistent with the theory that the Adventus Saxonum was a takeover by a small elite group of warriors, with very little change in the composition of the majority of the population.

The theory that the Anglo-Saxon invasion was merely a cultural change does not, on its own, explain why the native Britons adopted new Germanic modes of dress, language and religion (nor why the Picts adopted Scottish customs). The theory lacks a driver or catalyst for such changes; people are unlikely to adopt a new language, culture and style of dress on a mere whim. Perhaps raiding was the driving force for these changes. It would certainly explain how a small group of warriors could cause such widespread cultural and linguistic changes. Raiding by small groups of aggressive Germanic incomers could have destroyed the indigenous culture and eliminated the native elite. In the Roman period, across Cornwall and much of Wales native settlements do not seem archaeologically particularly ‘Roman’; after ad400, although there is evidence of site continuity, building plans change from round to rectangular, Latin inscriptions appear and there is evidence of Christianity. Perhaps the educated Romanized Christian elite (priests, lawyers and teachers, for example) from the lowlands fleeing raiding Anglo-Saxons arrived in western Britain, as was recorded by Gildas, Bede and the Life of St Wilfred. Those left behind in eastern Britain would perhaps want to adopt the cultural identity of the most hostile raiders (their mode of dress and language) in the hope they would be spared from attack.

Not only can these three different models for the respective Anglo-Saxon or Scottish takeovers of England and Scotland (population replacement, an elite warrior takeover and cultural change) complement the idea of widespread raiding, they are not mutually exclusive. While the evidence for violence from Anglo-Saxon cemeteries is rare, this does not preclude victims of raids being less likely to be carefully buried in organized cemeteries, or violence being rare but unpredictable and sporadic. The Anglo-Saxon settlement was probably a complex process, so that at different times and in different areas any of these three theories could best describe the process.

The outbreaks of sporadic raiding may have also helped with the spread of Christianity, which characterized the early medieval period. The Christian Church tried to control violence (for example, St Patrick’s letter to Coroticus, Adomnáin laws and wergilds in law codes) and while there are records of attacks on monasteries (as in the 645 reference in the Annales Cambriae), these were newsworthy to chroniclers possibly because they were shocking and rare. A society constantly plagued by uncontrolled violence is unlikely to grow economically or culturally. The prohibitions around attacking monasteries and churches would make invasions less catastrophic. Christianity, by creating rules around violence and places where killing was considered taboo, provided a brake on the more destructive elements of early medieval society, which made it attractive for kings to adopt and promote this new religion.


Like most human phenomena, the rash of early medieval dyke building and the raids that they were designed to halt probably had a beginning, a peak, a decline and then an end. With so few contemporary documents and so little unambiguous dating evidence from the dykes, we can only make very tentative conclusions about chronology. Sadly, we have more evidence for later reuses of dykes than for their original functions and the end of dyke building is probably easier to date than the origins, due to the lack of written evidence from the beginning of this period. For these reasons, the framework is discussed in reverse chronological order.

The early medieval dykes soon faded from memory from the ninth century onwards. Later people often reuse earthworks in very different ways to how their builders envisioned. Modern walkers use some early medieval dykes as footpaths (Offa’s Dyke and the Devil’s Ditch). Fieldwork has clearly demonstrated that farmers often use sections of dykes as field boundaries and this has probably gone on for centuries. The medieval scribes who wrote charters often use dykes as landmarks when describing estates. Early medieval people reused dykes as places to bury the dead. Perhaps after their abandonment they occupied a liminal area outside the control of kings and God where the condemned were executed; this would explain why so many are named after the Devil or pagan gods. There is little evidence that they were used (or reused) as meeting places, but equally we cannot be certain they were not.

As has already been speculated, the establishment of more stable kingdoms as well as the raids of the Vikings probably changed warfare forever. New raids came initially from abroad or were a part of wars between large stable kingdoms rather than by local warlords. These changes ended the use of dykes as military structures. When dykes were first built, warlords were raiding neighbouring areas to steal cattle. These warlords gradually set themselves up as kings, who then used raiding to force weaker neighbours to give tribute and/or submit to their overlordship. Gradually these evolved into more stable kingdoms, where rulers extracted surplus production from the land through large agricultural estates rather than raiding.

When the Vikings arrived, raiding resumed, but their raids were unpredictable. The first account of an Anglo-Saxon murdered by a Viking was at Portland in Dorset in 789, hardly the nearest British landfall from Scandinavia. Without obvious land routes to block, people ceased to excavate dykes across routeways. Early medieval rulers did not have the ability to mobilize enough manpower to guard an extended frontier, so they decided to construct points where their troops could hold up or sally forth from if the raiding force looked weaker than anticipated. These strongpoints are the burhs of the ninth century. Those dykes that already existed probably then became a nuisance to traders travelling along the routes that the earthworks blocked, so they were punctured where roads passed through the dykes. There does seem to be evidence that the Vikings carried on digging dykes like that at Reading, but they designed theirs to protect raiding parties rather than oppose them.

The radiocarbon and Optically Stimulated Luminescence dates suggest early medieval dyke construction peaked across the very late sixth and the first half of the seventh century. As Offa ruled 757–96, his dyke was probably constructed during the dying days of early medieval dyke building. The massive scale of his dyke and the labour involved could have outweighed any benefit it may have had in deterring Welsh raids. Perhaps this king (whose coinage and whose letters to Charlemagne demonstrate that he wished to be seen as a quasi-imperial ruler) made a massive and grandiose version of a common practical type of earthwork as a demonstration of his power. With better dating techniques, in the future we might discover that the larger earthworks are later in date and reflect the rise of kingdoms, even if this was probably not the original intention of the builders of most earthworks. Dyke building may have helped to create clearly defined kingdoms, but such stability may have signalled the end of the need for the shorter dykes to counter localized raiding.

The origin of early medieval dyke building in particular is more problematic. As this study found no early medieval dykes in the Highlands of Scotland, all the early medieval dykes were probably located in areas that at some point had been part of the Roman province of Britain. Presumably, the imperial authorities would not have allowed locals to build earthworks that blocked the Roman road network, so the dykes must post-date the end of Roman rule in Britain, say 400. If people could not predict the direction from which Viking attacks would come, presumably the same would be true of the early Anglo-Saxon raids from across the North Sea, or other seaborne raids from the north or west (the Irish, Scots or Picts). There is evidence that Iron-Age hill forts like Cadbury in Somerset were reoccupied in the immediate post-Roman period and perhaps these functioned in much the same way as burhs later did, as strongpoints against seaborne raiders (Cadbury was rebuilt as a burh). However, we should be cautious in assuming that every hill fort was reoccupied for military reasons; their association with the pre-Roman elite could also have been a draw.

Once the raiders from across the seas had established themselves in Britain and local people knew the direction their raids would take along known land routeways, dykes coupled with signal points would then have been the best form of defence. There is a great deal of debate as to when the Anglo-Saxons firmly established themselves in Britain, but from Bede onwards most historians have given a mid-fifth century date and we know from The Anglo-Saxon Chronicle that the Viking raids on Britain started in earnest in the ninth century. This gives a date range of roughly 450–850 for dykes to work against overland Anglo-Saxon raiding (though the British could have raided each other prior to this) and this is in fact a close match for the archaeological dates of early medieval dykes. Pre-Viking raiding logically peaked in this time bracket. The transition from refurbished hill forts to dykes then to burhs can be summarized in the diagram included here. Note that this diagram is partly based on (and indebted to) one made by Stuart Brookes and first publicly shown at a 2007 conference at University College London.

There are at least three possible inspirations for early medieval dyke building. Dykes may have been initially inspired by prehistoric earthworks; there are interestingly no prehistoric or early medieval dykes in Devon, while in Norfolk early medieval people seem to have reused the widespread pre-Roman earthworks. The fact that the Anglo-Saxons gave the name Grim (a god associated with war) to many prehistoric earthworks suggests they thought such dykes had a military purpose. The second possible inspiration (and the one most likely to have inspired the Britons) was the northern frontiers of Roman Britain. Roman signal towers, in particular those on the Yorkshire coast, may have inspired the signalling sites that I have postulated were associated with many early medieval dykes. The third possible source of inspiration for early medieval dyke building (and the structures most likely to have inspired Anglo-Saxon dyke builders) was the numerous dykes found in Jutland just prior to the Anglo-Saxons settling in Britain.

Forschungsmitarbeiter Mitch Williamson is a technical writer with an interest in military and naval affairs. He has published articles in Cross & Cockade International and Wartime magazines. He was research associate for the Bio-history Cross in the Sky, a book about Charles ‘Moth’ Eaton’s career, in collaboration with the flier’s son, Dr Charles S. Eaton. He also assisted in picture research for John Burton’s Fortnight of Infamy. Mitch is now publishing on the WWW various specialist websites combined with custom website design work. He enjoys working and supporting his local C3 Church. “Curate and Compile“
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