King Charles' Castle mid-16th century artillery castle and Civil War earthen artillery defence on western Castle Down, Tresco


Heritage Category:
Scheduled Monument
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Ordnance survey map of King Charles' Castle mid-16th century artillery castle and Civil War earthen artillery defence on western Castle Down, Tresco
© Crown Copyright and database right 2019. All rights reserved. Ordnance Survey Licence number 100024900.
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The building or site itself may lie within the boundary of more than one authority.

Isles of Scilly (Unitary Authority)
National Grid Reference:
SV 88270 16126

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.

Artillery castles were constructed as strong stone defensive structures designed specifically to house heavy guns. Most date from the period of Henry VIII's maritime defence programme between 1539 and 1545, though the earliest and latest examples date from 1481 and 1561 respectively. They were usually sited to protect a harbour entrance, anchorage or similar feature. These monuments represent some of the earliest structures built exclusively for the new use of artillery in warfare and can be attributed to a relatively short time span in English history. Their architecture is specific in terms of date and function and represents an important aspect of the development defensive structures generally. Although documentary sources suggest that 36 examples originally existed, all on the east, south and south east coasts of England, only 21 survive, all examples of which are considered to be of national importance. Two of these are situated on the Isles of Scilly: Harry's Walls on St Mary's and King Charles' Castle on Tresco; both originating in the same phase of fortification during the reign of King Edward VI. King Charles' Castle also formed the focus of a larger and later earthen artillery defence. Such defences were built in England between 1522 and 1683, partly overlapping with, and eventually superseding, the artillery castles some of which were incorporated into these later defensive forms. The earthen artillery defence comprises a bastioned earthwork with an outer ditch, sometimes faced with stone, designed both to house artillery and to protect a garrison, and sited to defend similar strategically-important locations as had the earlier artillery castles. Of an original 16 earthen artillery defences known to have been built, mainly along the south and the extreme north eastern coasts, only ten are known to have surviving remains. Of these, three examples are on the Isles of Scilly, forming a significant proportion of the surviving national resource of this class of monument.

The artillery castle at King Charles' Castle has survived comparatively well; despite the loss of the upper storey it displays clearly the essential details of its design and layout. The location of the monument near the mid 16th century earthen artillery defence across the northern half of Castle Down provides a rare survival of a wider defensive scheme in which artillery castles were intended to operate. The poor siting of this artillery castle and the evidence for remedial action as soon as it was built, in the form of the coastal blockhouse to the south west, gives a rare insight into how fortifications were planned in this period and the degree of central control and bureaucracy involved. This is strengthened by the breadth of surviving contemporary documentation detailing the wider context and detailed execution of this phase of fortification on the islands. The Civil War earthen artillery defence incorporating the artillery castle survives with an unmodified plan as one of the most complete examples of this very rare class of monument. Its relationship to the artillery castle and its much more extensive earthen artillery defence beyond the monument on Castle Down illustrates well the developments in fortification technique from the mid-16th to mid 17th centuries.


The monument includes a mid-16th century artillery castle, known as King Charles' Castle, situated on a slight hill at the western edge of the Castle Down plateau on northern Tresco in the Isles of Scilly. An earthen artillery defence was added to the north and east of the artillery castle during the English Civil War. The artillery castle is a Listed Building Grade II* and, together with the earthen artillery defence, forms a monument in the care of the Secretary of State. The artillery castle was built during 1550-1554 to command the northern entrance to New Grimsby Harbour, beyond the coastal scarp to the west between Tresco and Bryher. The castle has a cruciform plan with the hall and kitchen forming the eastern half, from which accommodation chambers project to the north and south, and with a semi-hexagonal gun platform extending to the west. The artillery castle has walls up to 1.65m thick, originally of two storeys but now surviving up to 3.4m high around the ground floor, and generally rising only 1.5m high. The walls have a granite rubble infill faced with randomly-coursed mortared rubble and with larger dressed slabs forming quoins and sills, jambs and lintels, which are mostly chamfered. Where they survive sufficiently intact, the windows generally have inner splays and the doorways have shallow, pointed arches of a type known as `four-centred' arches. The castle was entered by a small guardroom built onto the east wall of the castle. The guardroom is almost square, up to 3.5m across internally, entered by a doorway in the south wall. Beside the door was a recess in the inner wall-face and the guardroom was lit by a small window in the north wall. From the guardroom an arched doorway, with a draw-bar hole in its northern side, leads west into a large rectangular room measuring 8.8m north-south by 6m east-west. This room, occupying much of the eastern half of the castle, is now undivided but included the hall in its southern sector with the kitchen to the north. The hall was provided with a broad fireplace near the centre of the southern wall and was lit by rectangular windows to the south and east, the latter mullioned and partly blocked in a later alteration. The kitchen was lit by a single window in the north wall, with a pronounced asymmetrical inner splay. The kitchen's east wall contains a large fireplace, 1.85m wide and 1.7m high, with a massive edge-set lintel slab. An almost intact corbelled bread oven with a chamfered, arched doorway opens off the north side of the fireplace recess. Narrow doorways in the north and south walls of the hall/kitchen area lead to the two projecting accommodation chambers. Each chamber is similar, almost square in plan and measuring up to 2.9m across, lit by a small rectangular window in each of the three outer walls. The northern chamber also contains the rubble hearth of a small triangular fireplace across its south east corner. A doorway at the centre of the west wall of the hall/kitchen room leads to the castle's western ground floor gun platform. It measures 8.5m east-west by 8.9m north-south internally, its walls truncating the north west and south west corners to give it the semi-hexagonal plan. As originally built, the platform was provided with a gun port at the centre of each of the five outer walls, facing north, north west, west, south west and south. The gunports have almost square openings, averaging 0.5m across, splayed to the outer face only. The gunports open from rectangular recesses in the inner wall face, with remnants of paved hardstanding extending across the ground surface for up to 3.5m behind the gunports. The north east sector of the gun platform was partitioned off at a later date by a mortared wall, giving a subrectangular chamber measuring up to 4.5m east-west by 2.3m north-south. The former north-facing gunport was incorporated in the chamber's north wall and was widened to form a window. At the east end of the chamber, a doorway was broken through the former east wall of the gun platform to give access directly to the west side of the kitchen. The chamber was also provided with a small fireplace with a paved hearth, built into the partition wall in the south east corner. To the north and east of the artillery castle, an earthen artillery defence was erected around the crown of the low hill containing the castle during the Civil War, which on Scilly lasted from 1642-1651. The defence was designed to protect the castle from landward attack and encloses a subrectangular area measuring up to 60m east-west by up to 33m north-south internally, with the artillery castle in its south west corner. The defence is defined by a bank of earth and rubble up to 8m wide, up to 0.8m high internally and up to 2m high externally. The bank is accompanied by an outer ditch, up to 3m wide and 0.4m deep, and appearing flat-bottomed where best preserved on the north side, but obscured by silting in several sectors. The west and north sides of the bank are almost straight, the southern end of the west side extending from the rock outcrops immediately north west of the artillery castle. In the north west corner of the defence, the bank extends to define a pentagonal arrow-shaped projection called a bastion, allowing flanking fire across the sides. On the north east corner, the bank defines a projection similar in shape but truncated along the south east side, a feature called a demi-bastion. No bastion occurs on the south east corner but the east side is indented, giving that corner an acute angle. The south side of the defence's bank ends 22m east of the artillery castle, a gap which marks the site of the former entrance. Earlier plans of this monument indicate the presence of a broad triangular southern bastion covering this entrance and projecting from immediately south east of the artillery castle. The site of this bastion is now levelled and appears only as a slight scarp edging the gentle slope from the castle's walls. In addition to the surviving physical remains, our knowledge of this monument is amplified by surviving historical documentation and limited archaeological excavation. The artillery castle was part of a series of fortifications built on the Isles of Scilly during 1548-1554 in the reigns of Edward VI and Mary in response to a threat from the French. Garrisons were established on Tresco and St Mary's, but after an abortive attempt to construct an artillery castle on St Mary's, whose remains are known as `Harry's Walls', the emphasis of fortification in this phase focussed on Tresco. This artillery castle is mentioned in an account of the islands' fortifications dated May 1554, and in Privy Council Papers of 1558 the paymaster for this phase of fortifications, John Killigrew, was described as `captain in the Castell of Tresco'. The artillery castle is also depicted on a map of the islands drawn by John Davis in 1586. Despite its early prominence, the artillery castle was superseded as the islands' chief stronghold by the building of the Star Castle on the Garrison, St Mary's, in 1593-4. Several writers have observed that the artillery castle was poorly sited for its purpose of controlling the channel to the west. Being located on the crest of a scarp 40m above sea level, its location required its guns to fire down a very steep angle, which armament of the period was not designed to do. The castle was again garrisoned in the Civil War, by the Royalists who held the islands from 1642-6 and 1648-51. They strengthened the landward approach to the castle by the addition of the earthen artillery defence, but when the Parliamentarians retook Tresco, they simply by-passed the castle by landing on the opposite side of the island and besieged St Mary's from a battery on the southern tip of the island. The artillery castle was abandoned by its Royalist garrison in April 1651, one report stating that they blew it up on leaving. While this may account for some of the destruction of the upper storey of the castle, it is also considered that the castle was extensively dismantled for building stone to construct a blockhouse, now known as Cromwell's Castle, which was built in 1651-2 at the foot of the coastal scarp, 140m to the south west of this monument. Excavations within the castle in 1954 removed a considerable overburden of blown sand and revealed the interior choked by dumps of worked stone from the 17th century robbing episode, together with other such dumps around the outer walls of the artillery castle. These latter dumps are still visible, containing a spread of dressed stone including quoins, window splay fragments and sills, at least one from a mullioned window. Items recovered from these excavations have been used to construct two gun ports from the upper storey which are now situated on the floor in the western gun platform. The excavations also produced mid-16th century pottery, coins of Henry VIII and Edward VI, and a 16th or 17th century buckle. Beyond this monument, a second bastioned earthen artillery defence extends across Castle Down from 40m south east of the earthen artillery defence within this monument. The design of that earthen defence indicates that it was an unfinished outwork broadly contemporary with the building of the artillery castle and designed to extend the defensible area to include the whole northern half of the Castle Down plateau. The May 1554 account of the islands' fortifications also refers to a blockhouse under the castle on Tresco; although no visible remains are evident, it is considered that this earlier blockhouse was on the site of the later blockhouse built in 1651-2, 140m to the south west. That location better commands the channel between Tresco and Bryher, one of the routes of entry to the heart of the Scillies archipelago and the deep water approach to New Grimsby harbour, the main anchorage on Tresco, situated 900m along the coast to the south east. Situated close to sea level, that site would have complemented the artillery castle in this monument by removing the problem of having to fire guns steeply downwards, and indicates that this difficulty was realised early on in the life of this monument. King Charles' Castle lies very close to an extensive and dispersed cairn cemetery and linear boundaries to the east which are the subject of a separate scheduling. All English Heritage and Cornwall Archaeological Unit notices, fixtures and fittings, and modern laid surfaces are excluded from the scheduling but the ground beneath them is included.

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


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

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Books and journals
Borlase, W, Observations on Ancient and Present State of the Isles of Scilly, (1756)
Bowley, R L, The Fortunate Islands: A History of the Isles of Scilly, (1968)
Bowley, R L, The Fortunate Islands: A History of the Isles of Scilly, (1968)
Gill, C, The Isles of Scilly, (1975)
Gill, C, The Isles of Scilly, (1975)
O'Neil, BH St J, Ancient Monuments of the Isles of Scilly, (1960)
Ratcliffe, J, Fieldwork in Scilly 1991 and 1992, (1993)
Ratcliffe, J, Fieldwork in Scilly 1991 and 1992, (1993)
Ratcliffe, J, Fieldwork in Scilly 1991 and 1992, (1993)
Ratcliffe, J, Scilly's Archaeological Heritage, (1992)
Ratcliffe, J, Scilly's Archaeological Heritage, (1992)
Ratcliffe, J, Scilly's Archaeological Heritage, (1992)
Ratcliffe, J, Scilly's Archaeological Heritage, (1992)
Quinnell, N V, 'Cornish Archaeology' in A 16th century outwork to King Charles' Castle, Tresco, (1978), 142-3
Quinnell, N V, 'Cornish Archaeology' in A 16th century outwork to King Charles' Castle, Tresco, (1978), 142-3
Saunders, A D, 'Cornish Archaeology' in Harry's Walls, St Mary's Scilly; a new interpretation, , Vol. 1, (1962), 85-91
1358-0/1/116: King Charles' Castle, DNH, List of Buildings of Special Architectural or Historic Interest, (1992)
DoE/HBMC, AM Terrier and Deed Plan for King Charles' Castle, Tresco, (1984)
p71;1358-0/1/116 King Charles' Castle, DNH, List of Buildings of Special Architectural or Historic Interest, (1992)
Parkes, C/CAU, AM 107 for Scilly SMR entry PRN 7294.01, (1988)
Parkes, C/CAU, AM 107 for Scilly SMR entry PRN 7294.02, (1988)
Parkes, C/CAU, AM 107 for Scilly SMR entry PRN 7298, (1988)
Title: 1:10000 Ordnance Survey Map; SV 81 NE 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.

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