Prehistoric field system and hut circle north of Crab's Ledge, Tresco


Heritage Category: Scheduled Monument

List Entry Number: 1016422

Date first listed: 24-Sep-1999


Ordnance survey map of Prehistoric field system and hut circle north of Crab's Ledge, Tresco
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The building or site itself may lie within the boundary of more than one authority.

District: Isles of Scilly (Unitary Authority)

Parish: Tresco

National Grid Reference: SV 89709 13771


Legacy Record - This information may be included in the List Entry Details.

Reasons for Designation

The Isles of Scilly, the westernmost of the granite masses of south west England, contain a remarkable abundance and variety of archaeological remains from over 4000 years of human activity. The remote physical setting of the islands, over 40km beyond the mainland in the approaches to the English Channel, has lent a distinctive character to those remains, producing many unusual features important for our broader understanding of the social development of early communities. Throughout the human occupation there has been a gradual submergence of the islands' land area, providing a stimulus to change in the environment and its exploitation. This process has produced evidence for responses to such change against an independent time-scale, promoting integrated studies of archaeological, environmental and linguistic aspects of the islands' settlement. The islands' archaeological remains demonstrate clearly the gradually expanding size and range of contacts of their communities. By the post- medieval period (from AD 1540), the islands occupied a nationally strategic location, resulting in an important concentration of defensive works reflecting the development of fortification methods and technology from the mid 16th to the 20th centuries. An important and unusual range of post- medieval monuments also reflects the islands' position as a formidable hazard for the nation's shipping in the western approaches. The exceptional preservation of the archaeological remains on the islands has long been recognised, producing an unusually full and detailed body of documentation, including several recent surveys. Regular field systems are one of several methods of field layout known to have been employed in the Isles of Scilly from the Bronze Age to the Roman period (c.2000 BC - AD 400); closer dating within that period may be provided by the visible relationships of the field boundaries to other classes of monument with a shorter known time-span of use, or by their relationship with an earlier recorded sea level. They comprise a collection of field plots defined by boundaries laid out in a consistent manner, along two dominant axes at approximate right angles to each other. This results in rectilinear fields which may vary in their size and length:width ratio both within and between individual field systems. The fields are bounded by rubble walls or banks, often incorporating edge- or end- set slabs called orthostats. Within its total area, a regular field system may be subdivided into blocks differing in the orientations of their dominant axes. Regular field systems may be associated with broadly contemporary settlement sites such as stone hut circles. Some regular field systems on the Isles of Scilly contain a distinctive association, rarely encountered elsewhere, whereby certain of their field boundaries directly incorporate or link cairns, entrance graves and cists in some groups of prehistoric funerary monuments. Although no precise figure is available, regular field systems form one of the three principal forms of prehistoric field system, along with irregular field systems and some groups of prehistoric linear boundaries, which survive in over 70 areas of the Isles of Scilly. They provide significant insights into the physical and social organisation of past landscapes and they provide evidence for the wider contemporary context within which other nationally important monuments were constructed.

The prehistoric field system and hut circle north of Crab's Ledge survive reasonably well. The field system clearly displays its pattern and construction; it also shows the influence of the underlying topography in its orientation, with indications to the west of corresponding changes both in the local topography and the field system orientation. The hut circle on the slope of Crab's Ledge presents unusually clear remains for a surviving settlement site now in the inter-tidal zone, and provides valuable evidence for the nature and location of settlement in the now-submerged lower levels of the prehistoric landscape. The wider prehistoric land-use context is well illustrated by the contemporary settlement and field system survivals nearby around the coasts of southern Tresco. The peat formations closely associated with the field system are an unusual and rare survival whose analysis has provided valuable evidence for the date of the field system, its reason for abandonment and its environmental context. They have also made an important contribution to research on rates of sea level change that form a major influence on all aspects of human development on Scilly.


Legacy Record - This information may be included in the List Entry Details.


The monument includes a prehistoric field system and an associated hut circle surviving across the middle and upper shore between Crab's Ledge and the south coast of Tresco in the Isles of Scilly. The field system walls are intimately associated with three successive formations of early peat deposits exposed on the middle shore. The field system walls are visible as rows of rubble and small boulders, giving an overall width of about 0.5m-0.8m. In some walls the slabs are generally small, laid flat and almost level with the present shore surface; some others include closely spaced edge-set slabs, commonly 0.3m-0.5m high and 0.9m long, with their long axis usually along the wall line. The exposed area of the field system covers approximately 1ha and shows a rectilinear subdivision of the gently sloping surface between the present upper shore of Tresco and the inter-tidally exposed raised outcrops of Crab's Ledge. At least four roughly parallel walls, 20m-40m apart, run NNW-SSE down the shore, dividing its surface into broad strips. These walls are exposed over various lengths, the easternmost wall being visible over only 6m, while the next wall to the west extends for 100m to the edge of Crab's Ledge with various breaks in its visible continuity. The resulting strips are subdivided into long rectangular plots by occasional cross-walls on a roughly ENE-WSW axis, examples in the western half of the exposed area cross the strips roughly on the mapped line of Mean High Water, with others about 60m down the shore. A suggestion of finer subdivision occurs close to the north of Crab's Ledge, where two walls run WSW and about 18m apart from the longest of the downslope strip walls. The southern of these two walls runs up onto the raised area of Crab's Ledge itself; as it does so, it passes 1m north of a hut circle partly levelled into the slope. The hut circle has an internal diameter of 3.5m, defined by a rubble wall 1m wide and faced internally by edge-set slabs to 0.5m high; a similar facing is also evident along the wall's northern outer face. In the west of the scheduling, two walls extend west onto a boulder and rubble shelf from the line of the westernmost downslope wall. The northern of these has an ENE-WSW alignment, conforming with the other strip cross-walls, but the southern wall extends WNW for at least 26m, its alignment at odds with the rest of the exposed field system, and possibly reflecting an adaptation of the field system axis to changes in underlying topography as it approaches Sea Carn to the west. On the NNW, the field system's visibility extends to the points where its walling becomes masked beneath much later deposits on the upper and middle shore and by a sand dune behind them, though the field system's remains are considered to extend beneath those later accumulations beyond this monument. The limits of the field system's visibility on the east, south and west are defined variously by some masking by later shore deposits and by disruption of walling by wave action. On the upper middle shore, large exposures of early peat deposits extend across the northern sector of the field system's visible extent; another small exposure of an early peat occurs on the north west edge of Crab's Ledge itself, crossed by an isolated length of prehistoric walling near the south of the field system. Sampling of the northern exposures of peats during the early 1990s indicated three successive layers of peat formation, of which at least the uppermost is later than the field system walling that it abuts. Analysis of the peats showed a predominantly open vegetation in the vicinity and indicated their formation in coastal conditions, perhaps saltmarsh, whose effect on the soil would have ended the useful life of the of the low-lying fields that the walling defines. As radiocarbon dating has shown that the uppermost peat began to form in the later Iron Age or early Romano-British period, and continued accumulation into the early medieval period, the laying-out of the field system in this scheduling is demonstrably earlier than that date range. The level, origin and dating of this peat deposit has also been used to clarify estimates of the rate of sea level rise Scilly. Beyond this scheduling, further exposures of broadly contemporary field systems with settlement remains occur nearby along each side of Tresco's southern tip, in Bathinghouse Porth and Appletree Bay, and exposed on an old land surface beneath the dunes in the adjacent coastal cliffs.

MAP EXTRACT The site of the monument is shown on the attached map extract. It includes a 2 metre boundary around the archaeological features, considered to be essential for the monument's support and preservation.


The contents of this record have been generated from a legacy data system.

Legacy System number: 15501

Legacy System: RSM


Books and journals
Ratcliffe, J , Straker, V, The Early Environment of Scilly, (1996)
Ratcliffe, J, Sharpe, A CAU, Fieldwork in Scilly Autumn 1990, (1991)
Ratcliffe, J, Fieldwork in Scilly 1991 and 1992, (1993)
Parkes, C/CAU, AM 107 for Scilly SMR entry PRN 7345, (1988)
Plot on OS map by Cncl Isles Scilly, RCHME, 1:2500 RCHME plan of field systems at Crab's Ledge & B/hse Porth, (1997)
Tangye, M, Sketch plan of Crab's Ledge field walls, 1994, Unpubl sketch June 1994 in CAU record
Title: 1:2500 Ordnance Survey Map; SV 8913 Source Date: 1980 Author: Publisher: Surveyor:

End of official listing