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

A Scheduled Monument in Tresco, Isles of Scilly

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Latitude: 49.9638 / 49°57'49"N

Longitude: -6.3484 / 6°20'54"W

OS Eastings: 88267.921983

OS Northings: 16129.550124

OS Grid: SV882161

Mapcode National: GBR BXQS.6XM

Mapcode Global: VGYBX.X57M

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

Scheduled Date: 9 October 1981

Last Amended: 14 February 1997

Source: Historic England

Source ID: 1013667

English Heritage Legacy ID: 15411

County: Isles of Scilly

Civil Parish: Tresco

Traditional County: Cornwall

Lieutenancy Area (Ceremonial County): Cornwall

Church of England Parish: Isles of Scilly

Church of England Diocese: Truro


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
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
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
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
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.

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

Source: Historic England

Reasons for Scheduling

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'
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

Source: Historic England


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

Source: Historic England

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