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it was customary for the English to cut off the ears of every Welshman who was found to the east of the dyke, and for the Welsh to hang every Englishman whom they found to the west of it (1)

Offa's Dyke is a great linear earthwork whose construction is attributed to Offa, king of Mercia between the years 757 and 796, that stretches through the borderlands between Wales and England.


It is known as Offa’s Dyke after the association established by the ninth century Welsh scholar Asser who wrote in his Vita Regis Aelfredi (Life of King Alfred] 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
or in modern English,
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.

Despite some arguments about its exact dating (2) it is generally considered that Asser was essentially correct and that the Dyke is a genuine eighth century monument with construction beginning around 785 AD and continuing for several years afterwards. Although it is now considered unlikely that every stretch of the dyke that bears his name was actually commissioned by Offa, as he probably made use of existing stretches of earthwork at either end.


The entire English-Welsh border, from Prestatyn in the north to Chepstow in the south extends for some 150 miles (240 kilometres) and one of the sources of confusion is that the label Offa's Dyke gets used to mean both;

  • the entire presumed earthwork from coast to coast
  • the central section of some 80 miles (130 kilometres) from the Dee estuary in the north to the Wye Valley in the south

In any event the major stretch that survives extends from Coed Talon, near Treuddyn in Flintshire to Rushock Hill, near Kington in Powys but there are also fragments traceable further south in Herefordshire and in the Wye valley south of Monmouth.

The structure of the Dyke

The Dyke consists of a ditch and an earthen bank or rampart constructed with the ditch on the western, that is the Welsh facing side, but utilizing natural barriers wherever practicable. Although, to be honest, it is not known exactly what the Dyke looked like when it was first built, the available evidence suggests it was around 65 feet wide and 25 feet high from the ditch bottom to the bank top. The western side of the bank is believed to have been revetted with turf to create a near vertical face, and probably with some kind of palisade on top of the earthwork. It appears to have been constructed so as to provide an open view into Wales from along its length.


The existence of the Dyke is proof that the kingdom of Mercia possessed a high degree of cohesion in the late eighth century. A considerable degree of skill in engineering, planning and logistics would have been required to construct it with labour of thousands of men using only hand tools organized over many years.

It signifies an increasing level of political centralisation within Anglo-Saxon England and is the best surviving evidence of the power and achievement of Offa.

Its Purpose

The usual suggestion is to see the building of the Dyke as an attempt to rationalise a western boundary between the kingdom of Mercia and the independent Welsh kingdoms. The archaeologist Cyril Fox believed that the Dyke was the product of a negotiated agreement between Mercia and the Welsh Kingdoms.

It has however been noted that the Dyke cut through existing local administrative areas and seems to have made no difference to their boundaries that existed long afterwards. There were also regular gaps in its construction to permit normal agricultural practices to continue.

If the intention was to establish a border it was singularly unsuccessful, during the twelve hundred years since its construction the actual border between Wales and England has never borne any relation to the line of the Dyke.

More recently researchers such as Frank Noble and David Hill have advanced the view that the Dyke should be seen a specifically defensive earthwork built by Mercia to protect itself from a resurgent Powys and the threat of Welsh raids.(3) Although precisely how it would have operated as a defensive platform is not known. Mercia in common with other Dark Age British kingdoms had no standing army as such, and would have been unable to garrison the Dyke in any numbers. I any case, the subsequent history of the region suggests that the earthwork had only a short period of importance before being abandoned.

It is clear therefore that whatever Offa had in mind in ordering the construction of the Dyke he failed to achieve his objectives. Whilst Offa's Dyke is undoubtedly one of the great engineering achievements of the pre-industrial age and probably the most dramatic structure to have survived from the Anglo-Saxon age, it is also a monumental folly serving as a reminder of the limitations of royal power.


(1) As written by George Borrow in his Wild Wales, although the tradition seems largely to be of his own invention

(2) It has been claimed that the earthwork is the "lost" Roman wall of Septimius Severus on the basis of some rather imaginative interpretation of ancient texts for example.

(3) Not that it seems to have prevented Offa himself launching raids into Wales as the Annales Cambriae records.

(4) Sourced from the Clwyd-Powys Archaeological Trust at www.cpat.org.uk/offa/what.htm as well as www.offasdyke.demon.co.uk/ and www.castlewales.com/offa.html

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