Bolster Bank

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.

The Bolster Bank is a substantial univallate earthwork the central section of which survives particularly well. Lengthy linear earthworks of this kind are known elsewhere in England but the Bolster Bank is unusual in that it defends or demarcates a headland area rather than a spur or ridge, as is more common with cross dykes. The monument, the original length of which may be considered exceptional, will retain archaeological information, within both its bank and ditch, relating to its construction and use, and will offer information which will add to our knowledge of the division of the landscape in ancient times.

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.

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

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
Johnson, N, Cornish Archaeology in The Bolster Bank, St Agnes - A Survey, Vol. 19, (1980), 77-88

Other
Vyner, B, (1998)

End of official list entry

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