Offa’s Dyke

Asser, the Welsh biographer, and contemporary, of Alfred the Great, states:

There was in Mercia in recent times a certain king, who was dreaded by all the neighbouring kings and states. His name was Offa, and it was he who had the great dyke made from sea to sea between Britain [i.e. Wales] and Mercia.
Vita Alfredi §14
Offa’s Dyke at Edenhope, Shropshire, looking north.

There is no reason to doubt Asser’s word that Offa was responsible for the ditch-and-bank earthwork that bears his name – though there is, at the moment anyway (February 2024), insufficient scientific dating evidence to corroborate (or disprove) the statement. However, after some 1200 years of the activities of nature and, particularly, of people, it is only from Treuddyn (Flintshire) in the north to Rushock Hill (Herefordshire) in the south that a continuous earthwork is evident. (There is a gap of about five miles, north of Buttington, where the Severn apparently acts in lieu of the Dyke.) Indeed, in their Offa’s Dyke: History and Guide (2003), David Hill and Margaret Worthington, based on thirty years’ study of the Dyke, proposed that Asser’s assertion that it stretched “from sea to sea” should be considered to be “a literary device” (p.105), and that the sixty-four mile stretch from Treuddyn to Rushock Hill is in fact the full extent of Offa’s Dyke. They believed that other “intermittent and puzzling short lengths of bank and ditch” (p.107) between Rushock Hill and the Wye, to the west of Hereford, were nothing to do with Offa’s Dyke: “Although there are various short lengths of upstanding earthworks, when each was investigated from the air, with geophysical survey, with fieldwalking or with the spade, no continuous earthwork could be discovered and no connection could be made with Offa’s Dyke.” (p.143).  Recent work, involving the study of lidar data, however, has indicated that the Dyke really did continue from Rushock Hill to the Wye.[*]

Hill and Worthington dismissed the notion that “supposed earthworks” running north-south along the lower Wye valley in Gloucestershire were remnants of Offa’s Dyke,[*] but survey and reconnaissance has demonstrated that there was an earthwork, exhibiting build-characteristics similar to the earthworks of Offa’s Dyke, starting at Sedbury Cliffs on the Severn estuary, shadowing the Wye northwards and then turning eastwards.[*] Moreover, there is a reference dating from 1321 to part of this earthwork (to the west of St Briavels) as Offedich.[*] There remains, however, a large gap between this apparent southern section of Offa’s Dyke and the point where the central section seemingly picks-up west of Hereford.

It has traditionally been imagined that the Dyke must have continued northwards from Treuddyn to join the coast around Prestatyn. Various lengths of earthwork in that general direction have been called Offa’s Dyke, but when investigated have proven not to be. Some of these candidates have turned out to be prehistoric features, some post-medieval, and some belong to another massive linear earthwork called Wat’s Dyke [Map]. Recent reconnaissance, however, has raised the possibility that there is a route to be traced from Treuddyn, reaching the coast to the east of Prestatyn.[*]

WAT’S DYKE (the reason for the name is not certainly known) is some 40 miles long. It begins, in the north, at Basingwerk, on the Dee estuary, and then runs in a southerly direction, to the east of, and virtually parallel with, Offa’s Dyke, ending below Oswestry. “It is very similar to Offa’s Dyke, but better made”, says David Hill in British Archaeology (Issue 56, December 2000). It has generally been supposed that Wat’s Dyke was an earlier Mercian earthwork than Offa’s Dyke – Æthelbald (716–757) being popularly proposed as the work’s instigator – however, following an excavation in 2006, at Gobowen (Shropshire), OSL dating of samples from the ditch suggested that it was actually constructed in the early-9th century. If that is really the case, then Cenwulf, who became king following the very brief reign of Offa’s son, Ecgfrith, and who died at Basingwerk in 821, must be a strong contender for being the project’s ‘mastermind’.

Why these dykes were built and how they were operated are subjects of ongoing speculation.

See: Liam Delaney ‘Utilising Lidar Survey to Locate and Evaluate Offa’s Dyke’, in Offa’s Dyke Journal (the journal of The Offa’s Dyke Collaboratory) ‘Vol. 3 for 2021’, freely available online.
The Offa’s Dyke Collaboratory: “A Research Network for Offa’s Dyke, Wat’s Dyke and Early Medieval Western Britain”.
The 14th century reference to Offedich is reported in A History of the County of Gloucestershire* Vol. 5 (1996), p.249, the text of which is freely available online.
Hill and Worthington were evidently unaware of the above noted ancient reference. It was their belief that Cyril (later, Sir Cyril) Fox, who carried out fieldwork along Offa’s Dyke and Wat’s Dyke in the late 1920s and early 30s – his findings and opinions were published in 1955, under the title Offa’s Dyke: a Field Survey of the Western Frontier Works of Mercia in the Seventh and Eighth Centuries AD – invented (their word) the southern section of Offa’s Dyke: “he was wedded to the concept of Offa’s Dyke running from sea to sea, and he was therefore attempting to fill the perceived ‘gaps’.” (p.145).
* Founded in 1899 and originally dedicated to Queen Victoria, the VCH (Victoria County History) is an ongoing project to compile an encyclopaedic record of the traditional counties of England. Based at the Institute of Historical Research in the University of London since 1933.
Ian Bapty, who was at the time Offa’s Dyke Archaeological Management Officer for Clwyd-Powys Archaeological Trust, wrote a scathing review, titled ‘The Final Word on Offa’s Dyke?’, of Hill and Worthington’s book in which he criticized: “the overstretched presentation of ideas and interpretations as proven facts”.  Bapty writes: “their damning characterisation of this length as no more than slight and intermittent ‘supposed earthworks’ (p.146) with ‘little similarity to the form or siting of Offa’s Dyke in the undisputed central area’ (p.148) bears scant relation to the often massive, mostly continuous and generally impressive earthwork which anyone who visits Offa’s Dyke in Gloucestershire will actually find on the ground.”
Ian Bapty later teamed-up with Keith Ray to write Offa’s Dyke: Landscape and Hegemony in Eighth-Century Britain (2016), which acted as a catalyst for the formation of The Offa’s Dyke Collaboratory in 2017.
Optically Stimulated Luminescence dating: a technique in which the length of time that has elapsed since a mineral was exposed to daylight is determined.
See: Keith Ray, Ray Bailey, Tim Copeland, Tudur Davies, Liam Delaney, Dick Finch, Niall Heaton, Jon Hoyle and Simon Maddison ‘Offa’s Dyke: A Continuing Journey of Discovery’, in Offa’s Dyke Journal ‘Vol. 3 for 2021’, freely available online.