Two entrance graves, a prehistoric field system, and Civil War fieldworks and blockhouse on Innisidgen Hill and Helvear Down, St Mary's


Heritage Category: Scheduled Monument

List Entry Number: 1013271

Date first listed: 07-Oct-1976

Date of most recent amendment: 16-Nov-1998


Ordnance survey map of Two entrance graves, a prehistoric field system, and Civil War fieldworks and blockhouse on Innisidgen Hill and Helvear Down, St Mary's
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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: St. Mary's

National Grid Reference: SV 92208 12663


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.

Entrance graves are funerary and ritual monuments dating 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, the perimeter of which 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, spanning the walls. 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. Excavations within entrance graves have revealed cremated human bone and funerary urns, usually within the chambers but on occasion within the mound. Unburnt human bone has 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 in settlements, animal bone and artefact fragments. Entrance graves may occur as single monuments or in small or large groups, often 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. Regular field systems form one of several types of early field layout which occur close to entrance graves, and which is known to have been employed in the Isles of Scilly from the Bronze Age to the Roman period (c.2000 BC-AD 400). 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 size and length:width ratio within the field system. The fields are bounded by rubble walls or banks, often incorporating edge- or end-set slabs. 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 have a distinctive association, rarely encountered elsewhere, whereby certain field boundaries directly incorporate or link prehistoric funerary monuments, including some entrance graves. Although no precise figure is available, regular field systems form one of the principal forms of prehistoric field system 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 give evidence for the wider context within which other nationally important monuments were constructed. Civil War fieldworks on the Isles of Scilly are earthworks which were raised during military operations between 1642 and 1651 to provide temporary protection for infantry or to act as gun emplacements. The earthworks, which may have been reinforced with revetting or palisades, consist of earth and rubble platforms or banks and ditches. Three main types of Civil War fieldwork have been recognised on the Isles of Scilly: breastworks, batteries and platforms, which could be deployed separately or in combination to form a defensive complex. Breastworks are earth-and-rubble banks, up to 4m wide and 1.7m high but generally much smaller, which on the Isle of Scilly run beside the coastal cliff edge and are usually accompanied by a ditch along their landward side. Sixteen surviving breastworks are recorded on the islands. Batteries are a levelled area or platform, generally up to 20m across, situated on a hilltop or terraced into a slope to serve as a gun emplacement. They vary considerably in size and shape and are usually partially or wholly enclosed by a bank, occasionally incorporating one or two outer ditches. Twenty batteries survive on the Isles of Scilly, several connected by breastworks. Adjacent to some batteries are examples of the third fieldwork type, platforms. These are partly terraced into, and partly out from, sloping ground and represent sites of lookouts and temporary buildings. Eight such platforms, measuring up to 12m by 8m in size, are known to survive on the islands. The fieldworks were designed to defend the deep water approaches to the islands, especially St Mary's where most examples are found. Fieldworks are also known from Tresco, Bryher, Samson, St Agnes and Gugh. The circumstances of their construction are recorded in contemporary historical documents which indicate most were produced by the Royalist forces which controlled the islands for the entire Civil War period except during 1646-8. The Civil War fieldworks of the Isles of Scilly form a major part of the 150 surviving examples of fieldworks recorded nationally. They present an unusually complete system of fortifications from this period, both in the surviving range of fieldwork types represented and in the surviving pattern of their strategic disposition. The fieldworks and fieldwork complexes were occasionally associated with other classes of defensive monument, including blockhouses. Blockhouses are small, strongly-built defensive structures, built from the late 14th to mid 17th centuries and designed to house guns and protect the gunners and ammunition from attack. Blockhouses vary considerably in form, construction and ground plan but were typically sited as forward defences to cover anchorages, harbours, other defences and their approaches. Of the 27 blockhouses with extant remains recorded nationally, three are located on the Isles of Scilly, each of a different design, built during separate periods and for differing purposes, demonstrating well the diversity of this class of defensive monument.

The prehistoric entrance graves and field system in this monument have survived well. Despite some disturbance evident at both entrance graves, each displays clear evidence for its mode of construction, including unusual features such as the asymmetrical chamber in the south east entrance grave and the graded wall coursing along the chamber of the north west entrance grave. These features and their good overall survival have resulted in their frequent mention in reviews of this monument class. Their conjunction with a broadly contemporary field system illustrates well the unusual and distinctive integration of such funerary monuments into the farming landscape during the prehistoric period on the Isles of Scilly. The value of the relationships between the prehistoric features in this monument is amplified by the pollen evidence for the environmental context within which they were built. Further buried environmental data will typically survive within the considerable lynchet deposits of the field system. The Civil War breastwork, batteries and the blockhouse in the monument have survived well as an inter-related complex of fieldworks, despite some encroachment by the coastal cliff. Their situation and the survival of extensive documentation giving the historical context in which they were built demonstrate clearly the strategic methods employed by the Civil War military forces and the function of fieldworks within them. This is emphasised by the survival nearby of a series of complementary breastworks and batteries flanking this important maritime approach, of which the fieldworks in this monument formed an integral part.


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


The monument, on north eastern St Mary's in the Isles of Scilly, includes two prehistoric entrance graves, one near Innisidgen Carn on top of the spur forming Innisidgen Hill, the other on the lower northern slope of the hill, together with a prehistoric regular field system which occupies much of the northern flank of the hill. The monument also includes a group of fieldworks dating to the English Civil War. The fieldworks include a length of defensive bank and ditch, called a breastwork, which runs behind the northern and north east coastal cliff of Innisidgen Hill and extends south eastwards along the foot of Helvear Down to cross the landward side of Block House Point. Three small Civil War gun batteries are included at intervals in the line of the breastwork. At Block House Point the breastwork includes a defended approach to a broadly contemporary strongpoint called a blockhouse situated on the Point itself. The two prehistoric entrance graves and their immediately surrounding areas are monuments in the care of the Secretary of State. The south eastern entrance grave, on the spine of the Innisidgen Hill spur, occupies a prominent position on the narrow ridge top with the ground sloping away steeply to the north and south east. The entrance grave survives with a slightly ovoid mound of earth and rubble measuring 9m north-south by 8m east- west, set within traces of a flattened outer platform, up to 2m wide, whose outer edge is visible as a slight break in slope around all sides except the south and beside the entrance. The mound rises up to 1.8m high, with a shallow-domed, turf-covered upper surface, uneven due to an unrecorded antiquarian excavation and highest over the northern half of the mound. The mound has near vertical edges defined by a kerb, generally 0.7m high, built of both contiguous edge-set slabs and coursed slab walling, two to three courses high, but absent due to later robbing along parts of the southern side. The mound contains a well preserved chamber aligned on an ESE-WNW axis, with its entrance situated at the eastern side of the mound. The chamber measures 4.6m long by up to 1.5m wide and 1.2m high. The chamber walls are built of large edge-set slabs overlain where necessary, and all along the NNE wall, by coursed smaller slabs and rubble to remove the irregularities and produce a consistent chamber height. The WNW end of the chamber is closed by a single large edge-set slab. The walling gives a slightly asymmetrical chamber plan, with a straight NNE wall and curving, concave, SSW wall. The chamber is roofed by five large slabs, called capstones, up to 3m long, 1.1m wide and 0.6m thick, each resting on the chamber walls, spanning the chamber width, and laid side by side along the chamber from its WNW end-slab, leaving uncovered the eastern 1.25m of the chamber at the entrance. The capstones' upper surfaces are exposed in the mound surface along their southern sides and at the entrance. The other entrance grave in the monument is located 90m to the north west, near the foot of the northern flank of Innisidgen Hill. This entrance grave survives with a circular earth and rubble mound measuring 8.5m in diameter and rising up to 1.7m high from its downslope, northern edge. Parts of a peripheral kerb of single laid and edge-set slabs survive along the north, north east and east sides of the mound and flanking the chamber entrance on the SSW and SSE sides. The kerbing is up to 0.5m high and corresponds with a marked step in the mound's profile in those sectors. Except on the north, that step defines the edges of a shallow-domed central platform, 5.5m in diameter, with the mound's gentle outer slope extending a further 0.5m - 1.5m beyond the kerb. The mound contains a central chamber on a north south long axis with the entrance at the southern side of the mound's kerb line. The chamber measures 5.4m long by 1.3m wide and 1m high. Its parallel side walls are built mainly of coursed rubble, with an edge-set slab closing the northern end and large slabs incorporated into the central and northern parts of the east wall. The slabs forming the coursed walling over the southern 1.5m of the chamber are markedly smaller than those deployed elsewhere. Because the chamber floor is level despite the hillslope, near the southern entrance it is considerably below ground level and rises steeply to the southern edge of the mound. Two capstones survive, spanning the central and southern parts of the chamber, the largest measuring 2m long by 1m wide and 0.5m thick. The chamber of this entrance grave formerly contained an earth and rubble fill that was cleared during an unrecorded and unauthorised excavation in 1950. The prehistoric regular field system survives over 0.6ha of the northern slope of Innisidgen Hill adjoining the two entrance graves, extending over an area measuring at least 130m WNW-ESE by 60m NNE-SSW. The field system is defined by a network of earth and rubble banks, up to 2.5m wide and 1m high though commonly much slighter, aligned on two axes at approximate right angles to each other. At least six banks are visible on a WNW-ESE axis, almost along the contour but descending gradually to the WNW, while at least four banks with some incorporated slabs run uphill on a NNE-SSW axis, linking various of the other banks. The WNW-ESE `contour' banks are emphasised by a marked build-up of soil, called a lynchet, against their uphill, SSW, sides due to the effects of early cultivation on the steep slope. The southernmost `contour' bank merges with the northern edge of the outer platform around the entrance grave on the spine of the spur. Near the WNW edge of the field system, another such lynchetted bank, 0.5m high, extends ESE from the north east edge of the lower entrance grave. After several metres, this bank reaches a corner with one of the banks running uphill; to the east of this corner is a distinct original gateway gap before another contour bank appears, running to the ESE. Yet another lynchetted bank extends WNW from a point 5m beyond that lower entrance grave's south west edge. In addition to the surviving visible prehistoric remains, recent pollen samples from near Innisidgen Carn have indicated a vegetal history in this area involving clearance of early oak-hazel woodland, considered to have occurred during the prehistoric period. The clearance was succeeded by grassland with some cereal cultivation, followed later by the growth of heathland. The north western sector of the Civil War breastwork runs behind the coastal cliff of Innisidgen Hill, adjacent to the lower edge of the prehistoric field system. The breastwork survives as an earth and rubble bank, up to 1.5m wide and 0.7m high, with a ditch, up to 1.75m wide and 0.2m deep, along its landward side. Occasional larger rubble blocks, up to 0.4m across, are visible in the bank surface, the remains of a rough facing. The breastwork is visible over a distance of 520m, following an angular course combining several almost straight lengths closely following the line of the coastal cliff from Innisidgen Hill to Helvear Hill, with only minor breaks in the bank due to coastal erosion and one break of 30m to the north east of the lower entrance grave due to the creation of a recent slipway through the cliff. The breastwork incorporates three contemporary gun batteries in its line, 130m-150m apart. The north western battery is located 25m north west of the lower entrance grave, the central battery is below Innisidgen Carn, and the south eastern is midway between Innisidgen Carn and Block House Point. The batteries are visible as trapezoidal levelled platforms, 6m-18m wide and 3m-5m from front to rear, defined to each side by a sharp angle seawards in the breastwork bank, which extends along the forward edge of the battery and is increased in size, up to 3m wide and 1.4m high, with further traces of facing blocks. Due to their extreme cliff-edge situations, parts of the bank around the north western and south eastern batteries have been truncated by the eroding cliff edge. At the south east end of the monument, the breastwork across the landward side of Block House Point is broken by the constricted entrance to an approach way, flanked by extensions of the breastwork bank, to a blockhouse situated on the tip of the point. The blockhouse survives on a slight raised grassy knoll on the Point and is visible as a rectangular structure defined by earth and rubble walls on its north west, north east and south west sides, with a levelled internal area measuring 6m north west-south east by 5.5m north east- south west; the south east side is open. The turf-covered walls, 1m wide, rise to 1.9m high above the surrounding ground level and 0.8m above the blockhouse interior. The breastwork, batteries and blockhouse in this monument form part of an integrated system of Civil War coastal defences which survive extensively around St Mary's and include breastworks bordering potential landing places and near important settlements and installations, coupled with a system of batteries commanding complementary fields of fire over the waters around much of the island's coast. The breastwork in this monument provides cover over this relatively low-lying portion of coastal cliff, while the batteries command fields of fire over Crow Sound, the principal approach for shipping from the east into the Isles of Scilly. The blockhouse commanded a wide outlook over this important stretch of water. Beyond this monument, other broadly contemporary prehistoric field systems and settlement sites are recorded near the coast at Bar Point, from 275m to the north west, while prehistoric funerary cairns are located on Helvear Down, 120m south west of the monument's north west end and on Helvear Hill, 110m south west of the monument's south east end. The Civil War batteries complement the fields of fire of larger, more elevated batteries situated on Helvear Hill to the south and above Bar Point to the north west. Further lengths of breastwork also survive along the coast in both directions. All English Heritage signs, plinths and signposts, boundary markers and modern gravel surfaces are excluded from the scheduling, although the ground beneath is included.

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: 15400

Legacy System: RSM


Books and journals
Ashbee, P, Ancient Scilly, (1974)
Ashbee, P, Ancient Scilly, (1974)
Ashbee, P, Ancient Scilly, (1974)
Ashbee, P, Ancient Scilly, (1974)
Ashbee, P, Ancient Scilly, (1974)
Ashbee, P, Ancient Scilly, (1974)
Ashbee, P, The chambered Tombs on St Mary's, Isles of Scilly, (1963), 9-18
O'Neil, BH St J, Ancient Monuments of the Isles of Scilly, (1960)
O'Neil, BH St J, Ancient Monuments of the Isles of Scilly, (1960)
Thomas, C, Exploration of a Drowned Landscape, (1985)
Thomas, C, Exploration of a Drowned Landscape, (1985)
Thomas, C, Exploration of a Drowned Landscape, (1985)
Ashbee, P, 'Cornish Archaeology' in Bant's Carn, St Mary's: An Entrance Grave Restored And Reconsidered, , Vol. 15, (1976), 11-26
Ashbee, P, 'Cornish Archaeology' in Bant's Carn, St Mary's: An Entrance Grave Restored And Reconsidered, , Vol. 15, (1976), 11-26
Ashbee, P, 'Cornish Archaeology' in Bant's Carn, St Mary's: An Entrance Grave Restored And Reconsidered, , Vol. 15, (1976), 11-26
Ashbee, P, 'Cornish Studies' in George Bonsor: An Archaeological Pioneer From Spain On Scilly, , Vol. 8, (1980), 53-62
Dimbleby, G W, 'Cornish Studies' in A buried soil at Innisidgen, St Mary's, Isles of Scilly, (1977), 5-10
Dimbleby, G W, 'Cornish Studies' in A buried soil at Innisidgen, St Mary's, Isles of Scilly, (1977), 5-10
Evans, J G, 'Cornish Studies' in Excavations at Bar Point, St Mary's, Isles of Scilly, 1979-80, , Vol. 11, (1983), 7-32
Fowler, P J, Thomas, A C, 'Antiquity' in Lyonesse Revisited; the early walls of Scilly, , Vol. 53, (1979), 175-189
Saunders, A D, 'Cornish Archaeology' in Harry's Walls, St Mary's, Scilly: new interpretation, , Vol. 1, (1963), 85-91
Scaife, R G, 'Cornish Studies' in A history of Flandrian vegetation in the Isles of Scilly, , Vol. 11, (1984), 33-48
Scaife, R G, 'Cornish Studies' in A history of Flandrian vegetation in the Isles of Scilly, , Vol. 11, (1984), 33-47
Scaife, R G, 'Cornish Studies' in A history of Flandrian vegetation in the Isles of Scilly, , Vol. 11, (1984), 33-47
AM7 & Ancient Monuments Terrier for SI 352,
consulted 1994, Parkes, C, AM 107 for Scilly SMR entry PRN 7454, (1988)
consulted 1994, Parkes, C, AM 107 for Scilly SMR entry PRN 7454.01, (1988)
consulted 1994, Parkes, C, AM 107 for Scilly SMR entry PRN 7454.04, (1988)
consulted 1994, Parkes, C, AM 107 for Scilly SMR entry PRN 7455, (1988)
consulted 1994, Parkes, C, AM 107 relating to Scilly SMR entry for PRN 7453.01, (1988)
Parkes, C, AM 107 for Scilly SMR entry PRN 7454, (1988)
Parkes, C, AM 107 for Scilly SMR entry PRN 7454.03, (1988)
Parkes, C, AM 107 for Scilly SMR entry PRN 7456, (1988)
Parkes, C, AM 107 relating to Scilly SMR entry PRN 7453, (1988)
Parkes, C, AM 107 relating to Scilly SMR entry PRN 7453.02, (1988)
Rees, S E, AM7 scheduling documentation for CO 1031, 1975,
Saunders, AD, Recent Fortifications and Defences Works Assessment, 1992, Unpubl. draft, p.97; Innisidgen bl.
Title: 1:2500 Ordnance Survey Map; SV 9212 Source Date: 1980 Author: Publisher: Surveyor:
Title: 1:2500 Ordnance Survey Maps; SV 9112 & SV 9212 Source Date: 1980 Author: Publisher: Surveyor:

End of official listing