Ancient Monuments

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Offa's Dyke: section in Highbury Plains, 370m west of Birt's Barn

A Scheduled Monument in Trellech United (Tryleg Unedig), Monmouthshire (Sir Fynwy)

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Latitude: 51.7697 / 51°46'10"N

Longitude: -2.6709 / 2°40'15"W

OS Eastings: 353802.413056

OS Northings: 208100.577032

OS Grid: SO538081

Mapcode National: GBR FN.ZL3Z

Mapcode Global: VH871.NSC7

Entry Name: Offa's Dyke: section in Highbury Plains, 370m west of Birt's Barn

Scheduled Date: 24 September 1935

Last Amended: 24 April 2002

Source: Historic England

Source ID: 1020479

English Heritage Legacy ID: 33453

County: Monmouthshire (Sir Fynwy)

Community: Trellech United (Tryleg Unedig)

Traditional County: Gloucestershire


The monument includes the buried and earthwork remains of Offa's Dyke,
370m west of Birt's Barn, in Highbury Plains. 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 is visible as a bank with quarry pits. The bank
is about 10m wide at its base and stands to a maximum height of 2.5m on its
western face and 1m on its eastern face. To the east of the bank are a series
of quarry pits which are up to 8m wide and 0.4m deep. Deliberately laid
stonework has been exposed at intervals along the western face of the bank,
and may be interpreted as the remains of a dry stone revetment acting as a
near vertical, and highly visible, facing to the western side of the Dyke. The
lime kiln shown by the Ordnance Survey to the east of the line of the Dyke is
in a ruinous condition, and is thought to date to the 19th century.
The line of the Dyke is interrupted by a track which is now called Coxbury
Lane and is thought to be an ancient routeway leading to Wyegate, an early
medieval manor about 2km to the south of the point where the lane crosses
the Dyke at Highbury. Where the lane crosses the Dyke, it is included in
the scheduling.
All fences, fence posts, gates, stiles, sign posts and the remains of the
lime kiln are excluded from the scheduling, although the ground beneath
these features is included.

The site of the monument is shown on the attached map extract.

Source: Historic England

Reasons for Scheduling

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
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

The section of Offa's Dyke in Highbury Plains, 370m west of Birt's Barn
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.

Source: Historic England


Books and journals
Fox, C, Offa's Dyke: A Field Survey of the Frontier Works of Mercia, (1955), 187,234
Hoyle, J, Vallender, J, Offa's Dyke in Gloucestershire: Management Survay, (1997), 69-74
Maclean, J, 'Trans. of the Bristol and Glos. Archaeological Society' in The Course of Offa's Dyke in Gloucestershire, , Vol. XVIII, (1893), 26

Source: Historic England

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