How a Dyke could Counter Raiding
In 1959, Lieutenant-Colonel Alfred Burne published a paper arguing that Offa’s Dyke was more likely to be a military structure than an agreed frontier as Fox had suggested. Burne suggested that the reason why there were English settlements west of the dyke was that as an unmanned defensive structure, the Mercians needed sufficient warning to man the earthwork during a Welsh attack, while the other dykes of the Welsh borders were forward and rear lines of an integrated defensive system. Burne was not an archaeologist, but he was a respected military historian who knew about warfare. If we accept that raiding characterized early medieval warfare, we must examine how a dyke could prevent enemy forays entering the heart of a community.
Dykes could probably function in various ways in a society subject to raiding or the fear of raids. Finding a hostile raiding party in your territory and then intercepting it before it got away would be difficult. Such a raid would need to be ambushed before it could strike, so vulnerable communities blocked routeways with dykes. Dykes could deter attack by being so monumental in size that a potential attacker would deem the force needed to overcome the earthwork would outweigh any benefit from doing so. Dykes could also provide a fighting platform from which defenders could defeat raiders (monumental dykes that failed to deter an attack could obviously also be a place where defenders could make a stand). Communities could dig smaller dykes that were not a visible deterrent, but from which they planned to ambush attackers. Raiders resting before returning home could also dig an earthwork across a neck of land to defend a discrete area (like a peninsula) against counterattack. Similarly, defenders could make a peninsula defensible by use of an earthwork in order to have a refuge during a period when their community was under incessant attack; these last two functions potentially would give rise to very similar earthworks. If we examine these different functions in turn we can see how dykes fitted these four various scenarios.
The largest dykes are the most likely candidates for earthworks designed simply to deter attackers. The Devil’s Ditch, for example, is monumental in scale, rising up to 5m above the otherwise flat Cambridgeshire countryside. Kingdoms and communities to the west would undoubtedly have noticed such an earthwork, so while it would not have taken an attacker by surprise, it would certainly have made potential raiders think twice before attacking East Anglia. Equally, the sheer length of Offa’s Dyke meant that potential Welsh raiders must have been aware of it and they would have known that a king who could build an earthwork on such a scale was likely to have the resources to punish any attack on his territory. When the Welsh Annals record Offa devastating the British in 784, it was possibly a retaliation against Welsh raiding.
If these dykes failed to deter an attack, they could also have provided a platform to defeat raiders. Anyone who has tried to scale the Devil’s Ditch is surely painfully aware of how, if it was manned, it would be hard to overrun. Richard Muir, writing of the Devil’s Ditch, made the bizarre claim that: ‘invaders, charging in a column, would have overrun the dyke with ease. Despite the formidable appearance of the dyke, our tests showed that a fit young man could run from the outer edge of the ditch over the crest in less than half a minute.’ This is nonsense. It is very easy to lose one’s step on the bank and roll down to the bottom. As Allcroft put it: ‘Wet or dry, its smooth steep slope is as slippery as ice, so you are fain to go up on all fours, if at all.’ Even a slight blow from a defender would cause an attacker to tumble. I doubt that Muir’s runner was encumbered by shield, sword and spear. Today, the dykes are covered with grass and though we have evidence turf was used to stabilize the banks on some dykes, the ditches at least would have been muddy trenches. In damp weather, the soil would have clung to the attackers’ feet as they scrambled through the bottom of the ditch, slowing and tiring them as they tried to gain traction up the slope to where the defender lay in wait.
We can probably also dismiss Muir’s claim that the dyke would require too large a force to man, as the marvellous view from the top means that a relatively small force guarding it could easily send men along the bank to block any attempt to outflank them by raiders attacking at more than one point. Such a defensive strategy would not work so well with Offa’s Dyke, as its sheer length would surely make it easier for raiders to creep across an unguarded point. Perhaps Offa’s Dyke was deliberately set back from the border so that it could not be overrun by surprise (which is why English place names are found to the west) and some scholars have suggested that mounted guards could have patrolled it. Hill suggested that 100 mounted men in three shifts could patrol Offa’s Dyke, while beacons could summon defenders from nearby villages when they spotted Welsh raiders.
Mark Bell interestingly suggested that dykes were built by strong groups as a defence against more diffuse groups that they could not control; for example, we know that the stable kingdoms of China built walls against the Mongolian nomads to the north. This theory may explain why many dykes cluster round the powerful and aggressive kingdom of Mercia. Using this argument, perhaps we can suggest that powerful Mercian kings built the dykes of the Welsh borders to face pastoral Welshmen to the west, or perhaps powerful East Anglian rulers may have built the Cambridgeshire Dykes against diffuse groups to the west, which historians often refer to as Middle Angles (groups that were later absorbed into Mercia).
As the majority of dykes were much smaller than Offa’s or the Devil’s Ditch, they were less likely to deter attack, but communities may have built them as stop lines where raiders could be defeated (dykes like Grey Ditch in Derbyshire, Rowe Ditch in Herefordshire, Pear Wood to the north-west of London, for example). Most dykes are some way back from an actual frontier, so raiders could not easily overrun them, allowing defenders to assemble on the earthwork and plan their strategy before the attackers arrived. Many dykes cut Roman roads, or what charters tellingly refer to as herepaths or army paths, the very routes taken by raiders and invaders. The dykes in Glamorganshire, for example, seem to block ridges that give access from the uplands to the coastal plains (in an early medieval context this would mean keeping warriors from Brycheiniog out of Glywysing), often cutting ridges at narrow bottlenecks. Many of the smaller dykes required very few people to build them and some ‘rough dykes’ (which is the original meaning of the name of Rowe Ditch) were probably temporary measures thrown up at comparatively little notice. The need to build new dykes quickly to counter the threat of raids is possibly why the builders did not bother with a palisade. Raiders who successfully raided an unguarded community may have been surprised by a newly constructed earthwork blocking their progress when they had traversed the same route with ease the previous year.
We know from the complete lack of archaeological evidence of forts, watchtowers or fortified gateways that early medieval dykes were not permanently garrisoned, but, as scholars have suggested when discussing Offa’s Dyke, watchmen (like those mentioned in Beowulf or the speculators recorded by Gildas) may have patrolled them. These watchmen could then use beacons, flags, horns or messengers to warn the local people of the attack (if the raiders were burning farms as they came, the smoke may have made other warnings unnecessary). We know from later Anglo-Saxon documents that there was a system in each shire whereby the local lords could call on the services of their tenants to fight invaders. This was called the fyrd and earlier similar local organizations possibly existed across early medieval Britain. As the local men and the watchmen gathered at the earthwork, messengers could have sought out the local ruler and his warriors.
Previous scholars who have examined the dykes have not discussed the psychological influence of a dyke during a fight. It is likely that the defenders would be a group of (possibly terrified) locals lined up along the earthwork, whereas the attackers would more likely be warriors who derived their wealth and status from raiding. Morale is incredibly important in any battle; the local farmers protecting their land would be susceptible to reacting with panic and the biggest problem with inexperienced troops is that they tend to flee in the face of a determined attack. The attackers would probably travel on horseback to raid and dykes are very effective against cavalry, so would have inhibited the ability of mounted raiders to rout the defenders quickly. As the majority of casualties in battle happen when one side is in an uncontrolled flight, a ditch in front of the dyke which keeps the enemy at a safe distance would be a comfort to the defenders, while the bank would be a safety zone from which the defenders would be reluctant to flee. We know from the Battle of Hastings that manoeuvres like having the cavalry feign a retreat could draw out defenders from a secure position, upsetting defensive formations like a shield wall. Being on a dyke would discourage defenders from leaving their position – who would want to leave the security of an elevated position with good views for a flat field with hostile enemies, possibly mounted, pursuing you?
Perhaps the decapitated burials found at some dykes may have been the remains of defeated defenders who panicked or were overwhelmed by the superior numbers or skills of raiders. The defences of burhs later helped comparatively amateur defenders to see off attacks by semi-professional Viking raiders. In modern battles, most conscript soldiers never use their weapon; it is likely that in an early medieval context the defenders would probably hope that the enemy would simply go home. It probably takes four times as many troops to storm a defended position as to hold it, so the raiders would have to outnumber the attackers considerably before they dared to attack.
If the raiders decided to press on with their attack, a dyke would have many advantages for the defenders. The ditch would initially keep the raiders at a distance. Missile weapons (arrows, throwing axes and javelins) would potentially drive off an attacker without the need for the more terrifying prospects of close-quarter fighting. The defenders, if local farmers, would be less likely to own a shield and modern re-enactors state that it is difficult to wield a shield as well as the rather heavy Anglo-Saxon spear, so perhaps they did not form a shield wall on top of the dykes. Projectile weapons are far less effective when thrown or fired uphill, as the loss of momentum makes them easier to dodge and they will do less damage if they hit. If raiders were warriors who made their living from war, they were more likely to be armed with swords and the downward sweep of a heavy early medieval sword would be hard to manage against a defender raised up on a bank.
A dyke could also help to defeat as well as repel an attack. While the raiders, deep in hostile territory, were sustaining casualties assaulting the earthwork, messengers warning of the attack could be bringing more men to the aid of the defenders. If the defenders felt they had sufficient numbers, they could even use the earthwork to destroy the attackers, for example the men on the dyke could send out forays of more mobile and better-trained troops round the flanks of the raiders, then crush them against the dyke. The skulls found at dykes may not have been overwhelmed defenders, but the remains of a destroyed attacking force; perhaps their heads were mounted on stakes to deter other attackers. There are examples from early medieval sources across Europe that suggest displaying the body of an executed transgressor was considered normal. Individual earthworks have particular characteristics that would help to defeat an attacker. Minchinhampton Bulwarks cuts a ridgeway and the ends are located where the land slopes down to a valley; rather than being straight, the ends curve forward to form a reverse ‘C’ shape, effectively drawing raiders into the centre where the defenders will outflank them. Bokerley Dyke cuts a Roman road, but runs parallel to it for some distance, so that it can be used as a missile platform against attackers approaching from the north.
If the raiders sensibly avoided a frontal assault, even so outflanking the dyke may not have been as easy as modern fieldwork sometimes suggests. With a good map and stout boots on a peaceful sunny day it may be relatively simple to hike round the end, but it would not be so easy during a raid. As most early medieval dykes faced downhill and pollen or other environmental evidence suggest they ran across open country, defenders would have had a good panorama of the ground in front. This would not only give them good warning of attack, but during the fighting it would allow them to react quickly to any outflanking manoeuvre by the attackers. If the raiders tried to go around one dyke and rejoined the road, they may have faced another dyke, as many are found in groups, like those on Crookham Common. As the ends of many dykes are not obvious, a raider either had to send out patrols or guess which way was the best route round the earthwork. If a dyke deflected raiders off the herepath they were following so that they had to ford a large river or cross a deep gully, this would provide an ideal opportunity for an ambush. If a raider entered the wood or marsh on the flanks of a dyke, he would be entering an environment where the locals hunted and they could pick off the stragglers. As losses mounted (as raiders were wounded, killed or deserted), the leader of the raid would soon be forced to return to safety. It is likely that many raids were made at night, making it even harder to see the ends of the dyke or to navigate once the raiders had left the road.
The areas where there are no dykes are possibly ones where there was no need to build linear defences against raiders. The lack of dykes in central Mercia might be because the chronicles that record the hostile actions of Mercian kings like Offa and Penda, as well as archaeological evidence such as the Staffordshire Hoard, suggest that the Mercians did more raiding than their neighbours and it is only on their western frontier that they were being raided themselves. The border subkingdoms recorded in the Tribal Hidage that surrounded the core of the Mercian kingdom may have absorbed raids from other kingdoms. There are no dykes in north-west Wales, as mountains and tidal rivers that are hard to ford block access into the kingdom of Gwynedd. Big forests lay to the north of both Essex and Sussex (two shires devoid of early medieval dykes) and large tidal rivers or marshes cut their coastlines where defenders could ambush invaders as they attempted to ford these water obstacles. There are no dykes in the Highlands of Scotland, as there are few land routes worth cutting and most raiders would travel by boat.
The dykes built to protect headlands obviously do not block routeways, so perhaps some of these were dug as a defended beachhead by attackers on raids that required at least one overnight stop in hostile territory. We know that the Viking raiders used dykes to protect themselves from counterattack by digging earthworks across a narrow neck of land to make a safe haven, for example Coombe Bank near Reading. Perhaps Park Pale in Yorkshire is a Viking beachhead dug by Vikings attacking the kingdom of Northumbria. It is possible that Anglo-Saxon raiders constructed earthworks to protect themselves when resting during a raiding expedition, either before they settled in Britain or after. On the east coast of England Dane’s Dyke is the only earthwork that looks like a possible beachhead constructed by raiders from abroad and the twelfth-century Symeon of Durham claims that a seventh-century Anglo-Saxon king landed there. The source is unfortunately rather late, but the site is extremely well chosen and the earthwork’s massive scale makes it unlikely that it was a hurriedly built defence for a group of raiders.
There are problems with the idea that prior to the arrival of the Vikings dykes were built by raiders, but they might have been dug to defend against them. Large cliffs guard the seaward side of Dane’s Dyke and very late Roman signal towers along the coast to the north could have provided a warning of raiders, thus allowing the locals to gather their families and animals before retreating behind the dyke. Post-Roman finds and bodies with evidence of a violent death found at these signal stations support the idea that they may have acted with a fortified refuge at Dane’s Dyke to protect against raiders in the late and immediate post-Roman period. The earthwork at Heronbridge may have been a refuge or bridgehead for a marauding Northumbrian army, though it looks very well made to be a hurried defensive measure (in particular the careful reuse of Roman material in the revetment). With no gateways or signs of internal structures it does not resemble a fort, but looks like a beachhead defending a fording point. There are no dykes on the west coast of Britain that look like beachheads for Scottish or other Irish raiders; those in Cornwall are surely too long for a hastily erected defence. Therefore, though the Vikings may have used dykes as beachheads, there is little evidence that earlier raiders did, perhaps because their raids were swiftly concluded.
The Cornish dykes do not block routeways, but they do demark headlands, perhaps to defend against raiding, not from the sea but overland. In 815, The Anglo-Saxon Chronicle records the West Saxon King Egbert raiding Cornwall from east to west. The shorter dykes (like the one that delimited Stepper Point near Padstow) could have acted as refuges for large numbers of people and cattle. The larger dykes (like the Giant’s Hedge that runs between the Fowey and the Looe rivers) could be stop lines set back from a vulnerable border. The area it delimits is too large to just be a refuge, so it was probably designed to defend the core of a Cornish subkingdom, which is why it only covers a small part of the Hundred of West Wivelshire, yet it must have utilized labour from a larger area. The Cornish dykes are set back from the Tamar (and therefore the West Saxons) and beacons, for example St Agnes Beacon (a superb viewpoint enclosed by a dyke called Bolster Bank and visible from as far afield as Camborne), could have warned people to retreat behind the dyke. Similarly, at Tintagel a large ditch, probably early medieval in date, defended the settlement on the cliff-fringed peninsula from landward attack. Raiders could not outflank the Giant’s Hedge as it ended below the lowest fordable point on the Fowey and Looe estuaries. Peasant levies will often run in the face of raiders, but a dyke would give them confidence and a fixed point from which to make a stand, while raiders, always looking for easy targets, would leave a manned dyke alone. After the West Saxon raiders went home, the people could rebuild their ravaged farms.
Raiding was probably not always the norm in early medieval Cornwall. The archaeological record suggests a move away from the fortified settlements that characterized the Iron Age in Cornwall, suggesting that there must have been times of stability in the early medieval period. The dykes were temporary measures set back from the border built during times of crisis when the West Saxons threatened. As they rapidly fell out of use, locals soon forgot their names and stories of giants grew up to explain the origins of the Cornish dykes.
By not defending the Anglo-British border as the Britons of Dorset possibly had tried to do at Bokerley Dyke, the West Saxon kings could rampage along the spine of Cornwall, demonstrating their martial might while the Cornish were safe behind their dykes, having avoided being destroyed in a decisive battle. The Anglicization that occurred as Wessex expanded into Devon, Somerset and Dorset never occurred in Cornwall. Uniquely in south-west Britain, the inhabitants of Cornwall claim to possess a Celtic identity. Brythonic place names (especially in the central and western parts) abound in the Cornish entries of the Domesday Book and a Brythonic tongue was still the vernacular in western parts into the seventeenth century. The maritime links Cornwall maintained with Brittany up until the Reformation perhaps bolstered a Brythonic culture, but the south coast of Devon is as easy to reach by sea from Brittany, while north Devon and Somerset are only a short voyage from Wales. Control of Cornwall was certainly an attractive prospect to the kings of Wessex, as its mineral wealth had attracted merchants from as far away as the eastern Mediterranean from Phoenician times until the reign of the sixth-century Byzantine Emperor Justinian. The Tamar was never an impassable barrier and the English place names found in eastern Cornwall probably reflect West Saxon colonization of those parts of Cornwall nearest to Devon. The dykes may crucially have provided refuges, allowing Cornish society to weather the aggressive early stages of Anglo-Saxon expansion and so maintain their own identity.