Prehistoric chambered cairn 60m north of Knackyboy Carn, St Martin's


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Scheduled Monument
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Ordnance survey map of Prehistoric chambered cairn 60m north of Knackyboy Carn, St Martin's
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The building or site itself may lie within the boundary of more than one authority.

Isles of Scilly (Unitary Authority)
St. Martin's
National Grid Reference:
SV 92361 15863

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. Entrance graves are funerary and ritual monuments whose construction and use dates to the later Neolithic, Early and Middle Bronze Age (c.2500-1000 BC). They were constructed with a roughly circular mound of heaped rubble and earth, up to 25m in diameter, whose perimeter may be defined by a kerb of edge-set slabs or, occasionally, coursed stone. The mound contains a rectangular chamber built of edge-set slabs or coursed rubble walling, or a combination of both. The chamber was roofed by further slabs, called capstones, set across the chamber. The chamber was accessible via a gap in the mound's kerb or outer edge and often extends back beyond the centre of the mound. The cairn's mound and chamber may incorporate natural boulders and outcrops. Excavations in entrance graves have revealed cremated human bone and funerary urns, usually within the chambers but on occasion within the mound. Unburnt human bone has also been recovered but is only rarely preserved. Some chambers have also produced ritual deposits of domestic midden debris, including dark earth typical of the surface soil found within settlements, animal bone and artefact fragments. Entrance graves may occur as single monuments or in small or large groups, often being associated with other cairn types in cemeteries. They may also occur in close proximity to broadly contemporary field boundaries. The national distribution of entrance graves is heavily weighted towards the Isles of Scilly which contain 79 of the 93 surviving examples recorded nationally, the remaining 14 being located in western Cornwall.

The chambered cairn near Knackyboy Carn is one of the largest prehistoric cairns on Scilly and survives reasonably well, the excavation and earlier antiquarian activity being limited to the chamber and a section of the mound to each side. Most of the mound is unexcavated along with such funerary deposits and structures as have been confirmed beyond the south of the chamber and, sealed beneath the cairn, the early soil on which the cairn was built and which contained one of the rare neolithic artefacts to be recovered from Scilly. This is one of very few chambered cairns where undisturbed internal features have been recorded in sufficient detail to give a good understanding of the funerary and ritual activity that it embodied, the resulting information making a valuable contribution to our knowledge of these aspects and adding further to the importance of the unexcavated parts of this cairn. The huge pottery assemblage from the cairn contains a diversity of forms and decoration which provide an important source of reference for future studies of prehistoric pottery from south west England. The faience and glass beads from the chamber deposits are unique on Scilly and nationally very rare finds from this period, again marking out this cairn as highly unusual and enhancing the value of its unexcavated areas.


The monument includes a large prehistoric chambered cairn, of a type known as an entrance grave, overlooking the steep southern slope of western St Martin's in the Isles of Scilly. The cairn survives on the crest of the southern slope as a large ovoid mound, 19m north west-south east by 16m north east-south west, rising to 0.9m to a flattened upper platform. A slightly raised central area on the platform surface is defined by a low bedrock outcrop and at least three slabs from an inner kerb, roughly 7.5m in diameter and 0.4m high, within which is a shallow rectangular depression, 3m long east-west, denoting the cairn's funerary chamber. Although now largely covered by dense vegetation, excavation during 1948 in and immediately around the chamber has considerably increased our knowledge of this cairn's internal structure and the prehistoric funerary activity associated with it. The excavation revealed that the mound is built around a large bedrock outcrop which rises towards the centre of the platform. The cairn's funerary chamber is rectangular, measuring 3.7m long east-west by 1m wide internally and defined across the west end and the western part of its north side by faces of the bedrock outcrop. Beyond this, the north and south sides are walled by rubble set in a mortar made from the local granite subsoil and which extended over parts of the chamber's inner wall face; a portion of the north wall was disrupted by earlier antiquarian digging. The chamber entrance is on the east, constricted to 0.75m wide by flanking edge-set slabs. The chamber contained abundant and rich funerary deposits reflecting a complex sequence of ritual activity. The lower western end was levelled up and partly paved with flat slabs. Nearby, a hollow filled with charcoal and sand was overlain by a flat slab supporting a near-complete funerary urn; behind that two rows of three urns extended across the west of the chamber. Another urn stood at the centre of the chamber. All of these urns contained cremated bone fragments; the chamber's central urn also contained a glass bead and in the soil near that urn's base was a small star-shaped bead made of a greenish artificial material called faience, similar to a small number of such beads known from funerary monuments dating to the 2nd millennium BC mainly in southern England and Scotland. Spread around and partly over these urns was a thick deposit of charcoal, cremated bone and some soil, extending along and filling much of the chamber interior. Included within this deposit were large fragments of more urns, two small bronze artefacts and four rounded glass beads. The final deposition within the chamber comprised a further eight urns, complete or nearly so, placed onto that thick layer of charcoal, bone and artefacts: three were arranged along the midline at the centre and east of the chamber, with the others to each side. The excavation also found a separate focus of funerary activity beyond the chamber, 1m south of its western end, where two more urns were found within a small stone setting. Nearby and beneath the base of the cairn's rubble was a flint adze considered to be of neolithic date, earlier than the cairn and deriving from the old soil layer on which the cairn was later built. The cremated bone recovered from the excavation has been suggested as representing 60 - 70 individuals, accompanied by a very considerable amount of prehistoric pottery, over 200kg in total, much of which was decorated using incised lines or the impressions of comb-teeth or threads, and many urns bore handles formed as lugs, some of which are perforated. A further four small glass beads were also found during the excavation, not directly associated with recorded layers though closely comparable in form with those from the cairn's chamber.

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.

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Books and journals
Ashbee, P, Ancient Scilly, (1974)
Ashbee, P, Ancient Scilly, (1974)
Ashbee, P, Ancient Scilly, (1974)
O'Neil, BH St J, Ancient Monuments of the Isles of Scilly, (1949)
Thomas, C, Exploration of a Drowned Landscape, (1985)
Thomas, C, Exploration of a Drowned Landscape, (1985)
O'Neil, B H S, 'Antiquaries Journal' in The Excavation of Knackyboy Cairn, St Martin's, Isles of Scilly, , Vol. XXXII, (1952), 21-34
Butcher, S A, AM 7 & maplet for Scilly County Monument SI 850, (1971)
Thorpe, C/CAU, AM 107 for Scilly SMR entry PRN 7162.01, (1988)
Thorpe, C/CAU, AM 107 for Scilly SMR entry PRN 7162.02, (1988)
Title: 1:2500 Ordnance Survey Map; Cornwall sheet LXXXII: 15 Source Date: 1889 Author: Publisher: Surveyor: Both 1889 and 1908 editions
Title: 1:2500 Ordnance Survey Map; SV 9215 Source Date: 1980 Author: Publisher: Surveyor:


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 Digital, Culture, Media and Sport.

End of official listing

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