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Guest Author:
Keith Matthews
Stuart Laycock

Keith Fitzpatrick- Matthews was born in Letchworth, Hertfordshire, in 1958. He studied in Lancaster, and between 1985 and 1990 he worked as an archaeologist for North Hertfordshire Museums. Between 1990 and 2004, he worked for the Chester City Council, developing an extensive knowledge of the region’s archaeology. Since 2004 he holds the post of Archaeology Officer at the North Hertfordshire District Council’s Museums Service. He lives at Hitchin with his partner Bahkti. Home page.

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  The ‘Wall of Severus’
Keith J. Fitzpatrick-Matthews

One of the more startling claims for an early date for Wat’s Dyke and Offa’s Dyke has been made by the authors Steve Blake and Scott Lloyd[1], who propose that what has been known for the past thousand years and more as ‘Offa’s Dyke’ was in fact built by Roman armies during the reign of Septimius Severus (Emperor 197-211)[2]. They use literary texts and, as a ‘stop press’, the radiocarbon date for Wat’s Dyke, whose relevance is not immediately apparent. Interestingly, they hardly use archaeological evidence.

Their claim is based on their redesigned geography of Britannia/Ynys Prydein (which they perversely take to mean Wales, not Britain). They locate the Saxon invasion in Gwent[3], which they derive from the Ceint of the Historia Brittonum in contrast to the accepted derivation Venta>Guent>Gwent. They then take the Historia’s statement (Chapter 38) that illis regiones quae sunt in aquilone iuxta murum qui uocatur guaul[4] ‘those regions which are in the north, next to the wall that is called Gwawl’ with the earlier statement (Chapter 23) seuerus... murum et aggerem a mari usque ad mare per latitudinem brittanniae, id est per cxxxii milia passuum deduxit et uocatur brittannico sermone guaul[5] ‘Severus... built a wall and embankment from sea to sea across the width of Britain, that is for 132 miles, and it is called Gwawl in the British language’ and conclude that Severus built a defensive wall across Wales[6]..

Turning then to the Historia Augusta, a fourth-century compilation of Lives of various emperors from Hadrian to the later third century, they make the astonishing claim that “this one text alone forms the basis of our knowledge of the names of the Romans who built the Hadrian and Antonine Walls[7]. This does immense disservice to many years of archaeological investigation of the Walls, but no matter. They are more impressed with the statement in the Historia Augusta’s Life of Severus (xviii.2) that brittanniam, quod maximum eius imperii decus est, muro per transuersam insulam ducto utrimque ad finem oceani muniuit ‘he fortified Britain, which is a great ornament of his reign, with a wall led across the breath of the island to the edge of the Ocean on both sides.’ Again, at xxii.1, the Life mentions murum aut uallum... in Brittannia ‘a wall or rampart... in Britain.’

They attempt to translate Latin insula as ‘realm’, which is a completely unattested use of the word in a text written in the Mediterranean world, let alone Britain, but once again, let us pass over that. They criticise the consensus view that the documentary references to a Wall of Severus merely refer to a refurbishment of Hadrian’s Wall on the grounds that “the texts clearly state that there was a third Roman wall in the British Isles[8]. Once again, there is a problem that they gloss over: there is not one single text that states that there were three walls in Britain. Indeed, most insular texts are insistent that there are two Roman walls in Britain. Bede actually tackles this issue (Historia Ecclesiastica i.5[9] and i.12[10]); he knew from Orosius that Severus had built a wall, but he trusted Gildas more and accordingly distinguished the vallum of Severus from the later, nearby, murum of the fifth century. Of course, we now know Bede’s rationalisation of confusing statements to be wrong, but the term vallum (which means ‘wall’, just as murum does) has been retained for the curious earthwork feature to the south of Hadrian’s Wall.

Blake and Lloyd draw a number of conclusions from their reading of the texts[11]:

  • Septimius Severus built a defensive earthwork
  • It went from sea to sea
  • It was 132 milia passuum long
  • It separated Deifr and Alban

Having established this (at least, to their own satisfaction), they then turn to the Brut y Brenhinedd for evidence about the location of the Wall. They take its statement that Oswald, King of Northumbria, fought Penda, King of Mercia, at Maes Nafawl or Heavenfield, near Severus’s Wall. This derives from Geoffrey of Monmouth (Historia Regum Brittanie xii.10[12]), where the mistake of confusing the Battle of Heavenfield with the Battle of Maserfelth is first made. They do not spot the well-known error and instead castigate those who “have located this battle near Hexham... because of the reference to ‘the wall’, despite the fact that no evidence exists to back up this claim[13]. Evidently they have not read Bede (Historia Ecclesiastica iii.2)[14], where hagustaldensis ecclesiae… non longe abest, ‘the church of Hexham… is not far away’, written less than a century after the event. But never mind.

How do they pursue their quest for the true geography of Britannia/Ynys Prydein? They accept Geoffrey’s confusion and identify the Battle of Heavenfield, as a result of which Oswald became King of Northumbria, with the Battle of Maserfelth, at which he lost his life. They use the twelfth-century Vita Sancti Oswaldi to show that this battle was near Oswestry, Shropshire; a major earthwork frontier passes close to Oswestry: Offa’s Dyke. This, they argue, is Gwawl, the ‘Wall of Severus’.

They make a great deal of the length of the Wall of Severus given by Late Roman and Insular writers, where the figure cxxxii (132) milia passuum (Roman miles of 1,480 m) is generally given. This is about 195 km (slightly over 121 statute miles); Offa’s Dyke is around 192 km long (a little over 119 statute miles). The coincidence of length is impressive, it has to be said, even though there are only 130 km (81 statute miles) of earthwork. But what about the name?

Offa’s Dyke is first attributed to the King of Mercia (757-796) by Asser (Vita Regis Ælfredi Chapter 14), where it is said that fuit in mercia moderno tempore quidam strenuus atque uniuersis circa se regibus et regionibus finitimis formidolosus rex, nomine offa, qui uallum magnum inter britanniam atque merciam de mari usque ad mare fieri imperauit[15] ‘In recent times, there was a certain king in Mercia, vigorous and terrifying to all the kings and regions around him, Offa by name, who ordered a great wall to be built between Wales and Mercia, from sea to sea’. In the twelfth century, Giraldus Cambrensis (Descriptio Kambrie ii.7[16]) also attributed the Dyke to Offa.

Blake and Lloyd are worried by “how it was that the Saxons managed to build such a major structure whilst under constant attack from the Welsh and how a people with no history of building huge earthen banks... had the engineering skill to undertake such a vast project[17]. We can pass over in silence the Cambridgeshire Dykes, numerous other Early Saxon defensive earthworks as well as Wat’s Dyke, and ignore the evidence (such as the Annales Cambrie) that suggests that Offa was the aggressor, who constantly harried the Welsh. Moreover, as W H Stevenson pointed out in the notes to his edition of Asser’s Vita Regis Ælfredi, “the Germanic peoples were acquainted with such boundary ditches. Tacitus mentions the latus agger erected by the Angrivarii to divide their territory from that of the Cherusci. The famous Dannevirke was a similar boundary.[18] What Stevenson fails to point out is that the Danewirke was attributed to Offa of Angeln in a variety of sources (including Widsith[19]) and that Offa of Mercia may have deliberately emulated his famous putative ancestor in building a defensive dyke[20].

But what of the “Roman artefacts... found within the Dyke[21] that they believe prove its Roman date? This is an archaeological question, and one that they do not pursue. They evidently do not understand the concepts of the terminus post quem – the archaeological principle that states that no deposit can be older than the date of the most recent object found within it – and residuality – the idea that objects can turn up in deposits of much more recent date. These are important points, as they are crucial to understanding the radiocarbon evidence.

Having established the coincidence of length between Offa’s Dyke and the ‘Wall of Severus’/Gwawl, Blake and Lloyd start looking for documentary confirmation that the two are one and the same. They find it in an eleventh-century Irish translation of the Historia Brittonum known as Lebor Bretnach[22] (not “an Irish manuscript compiled in the eleventh century[23], since five separate manuscripts are known, ranging from an eleventh-century fragment down to full texts of the fifteenth and sixteenth centuries). The Irish translation of Chapter 23 of the Historia (Chapter 17 of Lebor Bretnach) states: Seuerus in treas ri tainic i mBretnaib. Is leis doronad clad Saxan a n-agaig na mBarbarda .i. Cruithneach. Da mile xxx ar c cemann ana fad, 7 is e ainm an claide sin la Bretnu Guaul, ‘Severus was the third king who came to Britain. He made the Saxon trench against the barbarians, i.e. Picts. It is 130 miles long and the name of the trench in British is Guaul’. Where the translator of Lebor Bretnach (an Irish scholar called Gilla Coemghin) got the description of Gwawl as being Saxon is unclear, but Blake and Lloyd see this as an important confirmation of their revised toponymy. They have no problem with the Picts bordering Offa’s Dyke, as they have already relocated them in North Wales (as they identify the historically documented people with the Gwyddyl Ffichti of Powys, mentioned only in one of the genealogies collected in the fourteenth-century Jesus College, Oxford, MS 20[24]).

However, Gilla Coemghin continues 7 roforcongair clod aili do denum a n-agaid Gaedeal 7 Cruithnech .i. clad na muice, ‘and he ordered another trench to be made against the Scots and the Picts, i.e. the Trench of the Swine’. This is interesting, and Blake and Lloyd do not quote it; Gilla Coemghin understood there to be two walls in Britain, so he corrects the Historia Brittonum and attributes the second wall to Severus, too. Whereas the first was called Guaul, the second is known as the Trench of the Swine. A variant of this name (Swine’s Dike) was recorded near Falkirk by the early eighteenth-century antiquary Horsley[25] as a local name for the Antonine Wall. It is important to note that here, the Cruithneach, ‘The Picts’, are associated not with North Wales, but with Swine’s Dike in central Scotland; we may assume that Gilla Coemghin believed that the same Picts were those associated with Guaul.

Notwithstanding this, Blake and Lloyd consider the case more-or-less proven at this point. They believe that Gilla Coemghin specified that the ‘Wall of Severus’ was clad Saxan, ‘the Saxon trench’ because he knew of Asser’s attribution of it to Offa over a century earlier. This does not seem very likely, as Asser’s Vita Regis Ælfredi does not seem to have been widely known. Still, there is “a stone inscribed to him that was found in Caernarfon, and it has also been suggested that he rebuilt the walls of Chester[26], which they take as evidence that the emperor was in Wales at some point. This is not sound historical deduction; an inscription uses the emperor’s name as a dating tool, while the hypothesis that the walls of Chester were rebuilt in his reign is not widely accepted today[27], nor would their rebuilding require his presence locally.

Finally, how did Asser come to misattribute the ‘Wall of Severus’ to Offa? Blake and Lloyd note that there are several placenames associated with both Offa’s and Wat’s Dykes that contain the name Offa. This is an error, they suggest, for Hengist’s cousin Ossa, “whose name is written in many manuscripts as Offa because of the similar appearance of the letters s and f in old manuscripts[28], although they do not suggest how palaeography might explain changes in placenames. The confusion, moreover, seems to be one that affects modern readers of medieval manuscripts and not one that affected their writers. There is a further historical problem, predictably. In Geoffrey of Monmouth (Historia Regum Brittanie vi.13)[29], following the Historia Brittonum (Chapter 38)[30], the names of the two relatives of Hengist given land near Guaul are Octha and Ebissa; the Brut changes Ebissa to Osla Gyllefawr, sometimes identified with the grandfather of Ida of Northumbria in the Historia Brittonum (Chapter 57)[31]. This is one of numerous changes made by the Brut to Geoffrey’s text, which derives much of its narrative from the Historia Brittonum; these changes are generally to bring the Brut into line with vernacular traditions[32]. Moreover, this character is Osla, not Ossa!

This is the evidence assembled by Blake and Lloyd in their reassessment of Offa’s Dyke and their attempt to show that it was built by the Roman emperor Septimius Severus. Their evidence consists almost entirely of documentary discussion, much of it using dubious sources, many of which are presenting information at second or third hand. The case for renaming Offa’s Dyke turns out not just to be weak, but wrong in the final analysis. The precise relationship of the radiocarbon date for Wat’s Dyke to their argument is never made clear, but it appears to rest on guilt by association. The hypothesis may be entertaining, but it is not supported by any good evidence.


[1] The Keys to Avalon: the true location of Arthur’s Kingdom revealed. Shaftesbury: Element (2000). I have placed a lengthy critique of this book on the web at http://www.kmatthews.org.uk/arthuriana/keys_to_avalon.html
[2] Dark, K R Civitas to kingdom: British political continuity 300-800. Leicester: Leicester University Press (1994), p. 224 raises the possibility that the Dyke is Roman or sub-Roman in date, only to dismiss it as improbable.
[3] Blake & Lloyd Keys, p. 56.
[4] Mommsen Historia Brittonum, p. 179.
[5] Mommsen Historia Brittonum, p. 165.
6] Blake & Lloyd Keys, pp 60 ff.
[7] Blake & Lloyd Keys, p. 62.
[8] Blake & Lloyd Keys, p. 62.
[9] Plummer Venerabilis Baedae, p.17.
[10] Plummer Venerabilis Baedae, p.27.
[11] Blake & Lloyd Keys, p. 63.
[12] Thorpe, L (trans.) Geoffrey of Monmouth: the History of the Kings of Britain. Harmondsworth: Penguin (1966), p. 277.
[13] Blake & Lloyd Keys, p. 64.
[14] Plummer Venerabilis Baedae, p. 130.
[15] Stevenson, W H Asser’s Life of King Alfred, together with the Annals of Saint Neots erroneously ascribed to Asser. New impression with article on recent work on Asser’s Life of Alfred by Dorothy Whitelock. Oxford: Clarendon Press (1959), p. 12.
[16] Thorpe, L Gerald of Wales: the Journey through Wales/the Description of Wales. Harmondsworth: Penguin (1978), p. 266.
[17] Blake & Lloyd Keys, pp 64-5.
[18] Stevenson Asser, pp 204-5.
[19] Alexander The earliest English poems, p. 39.
[20] Fox Offa’s Dyke, p. 289.
[21] Blake & Lloyd Keys, p. 65.
[22] van Hamel, A G (ed.) Lebor Bretnach: the Irish version of the Historia Brittonum ascribed to Nennius. Dublin: The Stationery Office, p.31.
[23] Blake & Lloyd Keys, p. 65.
[24] Evans, J G ‘Pedigrees from Jesus College MS 20’. Y Cymmrodor 8 (1887), 83-92, Genealogy XXIII p. 87.
[25] Horsley, J Britannia Romana; or, the Roman antiquities of Britain, in three books. London: John Osborn & Thomas Longman (1732), p. 172.
[26] Blake & Lloyd Keys, p. 65.
[27] Mason, D J P Roman Chester: city of the eagles. Stroud: Tempus (2001), p. 169.
[28] Blake & Lloyd Keys, p. 65.
[29] Thorpe Geoffrey, p. 161.
[30] Mommsen Historia Brittonum, p. 179.
[31] Mommsen Historia Brittonum, p. 202.
[32] Roberts, B F ‘Geoffrey of Monmouth, Historia Regum Britanniae and Brut y Brenhinedd. In: Bromwich, R, Jarman, A O H & Roberts, B F (eds) The Arthur of the Welsh: the Arthurian legend in medieval Welsh literature. Cardiff: University of Wales Press (1991), 97-116, p. 111.

The ‘Wall of Severus’ is copyright ©2001 Keith Fitzpatrick-Matthews, used with permission.

Comments to: Keith Matthews

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