Reasons for Designation
Cross dykes are substantial linear earthworks, typically between 2.2km and 1km
long and comprising one or more ditches arranged beside or parallel to one or
more banks. They generally occur in upland situations, running across ridges
and spurs. They are recognised as earthworks, as cropmarks on aerial
photographs, or as combinations of both. The evidence of excavation and
analogy with associated monuments demonstrates that the period of construction
of many cross dykes spanned the millennium from the Middle Bronze Age. Others
are known to have had a function in the Middle Ages; without excavation it is
difficult to determine whether this indicates reuse of earlier dykes or the
construction of new ones during the medieval period. Current information
favours the view that they were used as boundary markers, probably demarcating
some form of land allotment, although they may also have been used as
trackways, cattle droveways or defensive earthworks. Cross dykes are one of
the few monument types which indicate how land was divided up, whether in the
prehistoric or medieval period. They are of considerable importance for the
analysis of contemporary settlement and land use patterns. Relatively few
examples have survived to the present day and hence all well preserved
examples will merit statutory protection.
Details
The monument, which falls into three areas, includes the extant remains of a
linear earthwork referred to on maps of the 20th century as a Roman dyke, but
generally known simply as Bolster Bank. The earthwork originally enclosed
486ha of the St Agnes coastal headland, acting as a landward defence extending
for about 3.3km and linking two steep sided valleys, Chapel Coombe in the
south west to Trevaunance Coombe in the north east. Within the valley sides
the monument was defined by a low defensible terrace but elsewhere it was
represented by a bank and ditch. The bank utilised natural contours along
part of its length being highest and strongest in the central section where
the contours are gentle. It is this central section of the earthwork,
approximately one third of the original length of the monument, that is
included in the scheduling, the remainder having been levelled over the years.
The earthwork of Bolster Bank survives as a bank with an accompanying ditch on
its landward side. The bank survives to a maximum height of 3.4m and the ditch
to a maximum depth of 0.7m. The total width of the combined bank and ditch is
about 20m. Numerous gaps and breaches can be seen along the length of the
monument, most of which have been interpreted as later intrusions to
accommodate movement and access between the fields on either side of the bank.
The date of the Bank's construction has not yet been established with
certainty. Antiquarian sources favour a post-Roman date in the 5th or 6th
century AD, while a medieval document which gives the Cornish name Bothlester
(later Bolster) considered to derive from the upturned boat-shaped sections of
the bank, means it must predate 1398. A summary of all of the evidence
regarding the Bolster Bank was published by Nicholas Johnson in 1980. Later
research into linear boundaries similar to Bolster Bank has revealed that it
has more in common with medieval boundaries than with those of earlier
periods. The rich tin resources on the St Agnes headland, which would
only have become available to mining from the medieval period onwards, provide
one possible reason for the construction of the Bolster Bank in demarcating
and protecting a valuable area of land.
Excluded from the scheduling is all fencing, fence posts, gates and gate
posts, and all telegraph poles, although the ground beneath these features is
included.
Legacy
The contents of this record have been generated from a legacy data system.
Legacy System number:
29669
Legacy System:
RSM
Sources
Books and journals Other
Legal
This monument is scheduled under the Ancient Monuments and Archaeological Areas Act 1979 as amended as it appears to the Secretary of State to be of national importance. This entry is a copy, the original is held by the Department for Culture, Media and Sport.
End of official list entry
