Reasons for Designation
Offa's Dyke is the longest linear earthwork in Britain, approximately 220km,
running from Treuddyn, near Mold, to Sedbury on the Severn estuary. It was
constructed towards the end of the eighth century AD by the Mercian king Offa,
and is believed to have formed a long-lived territorial, and possibly
defensive, boundary between the Saxon kingdom of Mercia and the Welsh
kingdoms.
The Dyke is not continuous and consists of a number of discrete lengths
separated by gaps of up to 23km. It is clear from the nature of certain
sections that differences in the scale and character of adjoining portions
were the result of separate gangs being employed on different lengths. Where
possible, natural topographic features such as slopes or rivers were utilised,
and the form of Offa's Dyke is therefore clearly related to the topography.
Along most of its length it consists of a bank with a ditch to the west.
Excavation has indicated that at least some lengths of the bank had a vertical
outer face of either laid stonework or turf revetment. The ditch generally
seems to have been used to provide most of the bank material, although there
is also evidence in some locations of shallow quarries. In places, a berm
divides the bank and ditch, and a counterscarp bank may be present on the lip
of the ditch.
Offa's Dyke now survives in various states of preservation in the form of
earthworks and, where sections have been levelled and infilled, as buried
features. Although some sections of the frontier system no longer survive
visibly, sufficient evidence does exist for its position to be accurately
identified throughout most of its length. In view of its contribution towards
the study of early medieval territorial patterns, all sections of Offa's Dyke
exhibiting significant archaeological remains are considered worthy of
protection.
The section of Offa's Dyke in Highbury Plains, 770m south west of
Glyn Farm survives well, and illustrates the use of natural topography to
enhance the form and visibility of the Dyke. The bank will have preserved
part of the original ground surface, predating the construction of the
monument and, along with the quarries, will contain environmental
evidence in the form of organic remains which will relate both to the
Dyke and to the landscape within which it was constructed. The bank will
also contain evidence relating to the methods of construction of the
monument as well as the building materials used.
Details
The monument includes the buried and earthwork remains of Offa's Dyke,
770m south west of Glyn Farm. Offa's Dyke generally consists of a bank
up to 3.5m high with an intermittent ditch to the west and quarry ditches to
the east. In places, Offa's Dyke was strengthened by additional
earthworks, namely a berm between the bank and ditch, and a counterscarp
bank on the western lip of the ditch.
In this section the Dyke runs for some 284m and is visible as a bank with
quarry ditches to the east. The bank runs along the edge of a steep slope and
is between 4m and 12m wide at its base, standing to a maximum height of 2m on
its western face and 0.8m on its eastern face. The quarries, from which
material was excavated during construction of the monument, are between 4m and
8m wide and up to 1m deep. The narrowness of the bank in places may be due
to later quarrying, which appears to have taken place throughout this area.
MAP EXTRACT
The site of the monument is shown on the attached map extract.
