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St Mawes Castle

A Scheduled Monument in St. Just-in-Roseland, Cornwall

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Latitude: 50.1554 / 50°9'19"N

Longitude: -5.0239 / 5°1'26"W

OS Eastings: 184089.728363

OS Northings: 32748.187585

OS Grid: SW840327

Mapcode National: GBR ZH.G9J4

Mapcode Global: FRA 08CL.W14

Entry Name: St Mawes Castle

Scheduled Date: 9 October 1981

Last Amended: 10 July 1996

Source: Historic England

Source ID: 1013807

English Heritage Legacy ID: 15420

County: Cornwall

Civil Parish: St. Just-in-Roseland

Built-Up Area: St Mawes

Traditional County: Cornwall

Lieutenancy Area (Ceremonial County): Cornwall

Church of England Parish: St Just-in-Roseland

Church of England Diocese: Truro


The monument includes an early 16th century artillery castle at St Mawes, on a
broad headland flanking the east side of the Carrick Roads, the mouth of the
River Fal, on the south coast of Cornwall. The wider curtilage of the
artillery castle incorporates a broadly contemporary shoreline blockhouse;
from the 17th to 20th centuries the slopes of the headland around the
artillery castle were modified by successive phases of gun batteries. Also
included among the ancillary structures is a series of World War II
searchlight emplacements immediately beyond the headland's coastal revetment
wall. Powder and ammunition magazines were also built into the headland's
lower slope during the mid and late 19th century. A late 17th century lead-
covered dome, called a cupola, was added to the castle's stair turret as a
daymark - a maritime navigational aid. The blockhouse, artillery castle,
magazines and outer defences in this monument are Grade I Listed and this
monument is contained within a wider area in the care of the Secretary of
The date of the shoreline blockhouse is not precisely known. Certainly
complete by the period 1547-53, it may be the earliest fortification in the
monument, built in the late 1530s to strengthen the defences of the Fal
estuary as a preliminary local response to threats of attack from France and
Spain in the immediate aftermath of the English Reformation. It survives as a
semicircular building of local stone, 17m in diameter, on a rock-cut stance
on the shoreline fringing the headland. Its curved wall, c.3m thick, projects
south west towards the Carrick Roads and is pierced by three arched gun ports
fronting vaulted recesses, called casemates; a former fourth gun port facing
north west is blocked. In the south east of the blockhouse is a large raised
oven with part of its domed roof and door intact, and the base of a water
cistern. Remains survive of the blockhouse's thin rear wall, set slightly
apart from the straight vertical rock-cut face behind the building. A former
upper gun platform and battlements have not survived.
In the spring of 1540, work began on the much more substantial artillery
castle 50m north east of the blockhouse, on a levelled stance higher up the
headland slope. The castle was part of Henry VIII's rapid upgrading of the
nation's defences along the south and south east coasts in response to
intensified threats of invasion from France and Spain. It was built under the
direction of Thomas Treffry, a prominent landowner and merchant from the port
of Fowey, employing a design imposed centrally and incorporating many
distinctive elements shared by other artillery castles of this phase.
Completed in 1543, the artillery castle consists of a circular central tower,
the keep, rising above and abutted by three part-circular bastions: two are
side bastions, to the north west and south east, and one is a forward bastion,
to the south west, giving a `clover-leaf' plan. North east of the castle is a
dry moat crossed by a bridge from a guardhouse. The castle is built in local
slatestone rubble with granite employed for quoins, coping, string courses,
dripstones and frames for doors, windows, gun ports and casemates. The high
quality of the castle's architectural finish is supplemented to an unusual
degree by a range of carved and incised decorative features. These include the
Royal Arms, in high relief over the entrance to the keep and in low relief,
accompanied by carved sea monsters, over the door from the keep to the forward
bastion. Other features include blank shield plaques set into the bastions'
outer walls, gargoyles on the keep's upper string course and dedicatory and
laudatory inscriptions to Henry VIII, composed by the King's Chaplain and
Antiquary, John Leland.
The guardhouse is a single storey building, up to 8m across externally.
Originally octagonal, it was reduced to an asymmetric hexagonal plan in the
18th century and now has a modern slate roof and chimneys over the north west
and south east angles. Its shallow-arched entrance is in the east wall; the
other outward-facing walls each bear a cruciform musketry loop. Between the
guardhouse and the bridge over the moat is a subrectangular walled yard, up to
6m wide and 18m long internally, which housed the castle's stabling after the
guardhouse had been modified.
The dry moat is up to 7.5m wide and rock-cut, with a small reservoir for the
castle's water supply cut into its outer, north east face, fed by a spring.
The moat is crossed by a two-arched bridge broadly contemporary with the
castle; although the keep has chain slots for a drawbridge, this may not have
been installed, as an engraving drawn between 1547 and 1553 shows the
two-arched bridge in place.
The keep is 14m in external diameter, with walls up to 2.45m thick, rising
through a circular basement and three octagonal floors to an open gun platform
on the roof. The deeply-moulded arched main door, accessed from the bridge, is
on the second floor; this floor formed accommodation for the castle's governor
and chief officers, partitioned to give small rooms in the north and east
quadrants and a larger room occupying the south west half of the floor. Each
room is provided with a fireplace and windows face north west and south east.
Some original oak door heads survive, carved with foliage, figures and
inscribed scrolls dedicated to King Henry VIII and Prince Edward. To the south
of the main door is a stone winder stair extending throughout the height of
the keep.
The first floor was formerly also partitioned into three accommodation rooms
and used by the ordinary soldiery of the garrison, though its internal walling
has not survived; the former small north quadrant room on this floor has a
private latrine or possibly an armourer's store, lit by a partly-blocked slit
Below these accommodation floors, the basement housed the kitchen, whose paved
floor contains slab-covered drainage channels and includes two granite posts
supporting the beams of the floor above. The large kitchen fireplace is at the
south west, with a brick-lined bread oven opening off its south side. A
granite pedestal considered to have supported a water basin is located by the
opening from the stairwell to the kitchen.
Above the accommodation floors, the third floor is the upper gun deck,
unpartitioned, with vaulted recesses and small raised gun ports, now glazed,
in each of its eight sides to house hand guns. Each recess has an ammunition
cupboard in one side and a blocked smoke vent in the roof. On the north east
this floor has two low-level slits beneath the gun port to carry drawbridge
chains, if they were ever installed; slots called `murder holes' also
perforate the gun deck floor over the keep's entrance arch.
The roof of the keep, now lead covered, was originally a circular gun platform
whose battlemented wall has seven widely splayed embrasures - these alternate
with the positions of the gun ports below in the upper gun deck, except at the
ENE where a slender circular turret rises as a lookout point, reached by an
extension of the keep's winder stair. The present lead covered pointed dome
with a bulbous finial was added to the turret in the later 17th century to
create a highly visible and unmistakable feature called a day mark, which
mariners could recognise when navigating nearby waters. The 1547-1553
engraving shows this replaced a smaller dome on a battlemented turret wall.
The side bastions abutting the north west and south east of the keep are each
of similar part-circular plan, 16.4m in external diameter, rising to a parapet
meeting the keep between its second and third floor levels. The side bastion
ground floors are entered by passages through the wall thickness from the
forward bastion and are open paved courtyards, though several features
indicate an original intention to roof them. Their ground floor walls are
pierced by gun ports with large vaulted casemates; these housed cannon except
for those facing into the dry moat which are provided with cruciform musketry
slots. The north west bastion's courtyard contains a 19th century water
hand pump from the later use of the castle. The parapets along the top of the
side bastions are finished with battlements whose widely splayed embrasures
contain pivot-beam slots for hand guns and sockets for shutters. The parapets
are served by a wall walk entered on one side through doors in the keep's
upper accommodation floor and on the other from steps passing through the
keep's wall from the forward bastion; the steps to the south east bastion pass
by a latrine built into the keep's wall.
The forward bastion is slightly lower than the side bastions which its walls
abut. It is also part-circular in plan, 18m in external diameter, and had two
gun floors. The ground floor is entered by an arched doorway from the keep's
lower accommodation floor and forms the castle's main gun deck, provided with
vaulted casemates in the wall thickness for cannon. Its upper floor formed a
raised gun platform for cannon, though the present flooring is modern. This
raised platform gave a longer range for cannon which fired through embrasures
in its battlements.
The wider curtilage of the castle expanded over the following four centuries
as gun batteries and related structures were moved out from the castle's built
structure and came to occupy the coastal slope of the headland's tip below and
to each side of the castle buildings, resulting in the system of terraces and
ramps that are visible over most of the slope. Early stages in the development
of that system are evident from 17th and 18th century documents and
illustrations. A survey of 1623 mentions `earthworks' built outside the side
bastions, probably the levelled platforms, still surviving, that adjoin these
bastions and which are evident on a 1734 engraving by the Buck brothers. The
engraving also shows gun batteries along a revetted coastal edge extending in
both directions from the coastal blockhouse, an area known as the Lower Gun
Battery and known to have been used as the principal battery since the 17th
century. At the end of the 18th century, during the Revolutionary Wars with
France, the shoreline blockhouse was re-armed and at the Lower Gun Battery, a
twelve-gun battery was built with three flanks, facing south west, SSW and
SSE. The battery was provided with an earthen rampart, up to 2.5m high and 7m
wide, backed by a vertical rubble wall; the SSE flank retains its arrangement
little modified whereby the cannon fired through embrasures in the wall, lined
by granite quoins, and were mounted on traversing gun carriages running on two
sets of curved rails. On the other flanks, the inner carriage rails mostly
survive but the outer rails have been removed and the embrasures blocked.
After this upgrading of the Lower Gun Battery, in the early 19th century, a
magazine was built to improve its ammunition supply. It is concealed by being
cut deeply into the terrace behind the battery, from which it is separated and
further hidden by a remnant strip of the terrace scarp. The magazine is a
rectangular building, 11m long by 5.5m wide, with a double-skin ventilated
wall and porched doors at each end leading to separate powder and shell
stores. Its low pitched roof has granite coping and is covered by earth and
turf to absorb shell fire. Angled passages lead from the magazine to the
Lower Gun Battery and a steep flight of steps descends to the magazine from
beside the forward bastion of the Henrician castle.
In the mid-19th century, a small laundry and bath house were built on the
midslope terrace beyond the south east bastion of the Henrician castle; these
were demolished in 1920 but their site and foundations form the basis of a
modern fishpond.
About 1870, the Lower Gun Battery was armed by four 64 pounder guns but these
were soon obsolete. To cover effectively a submarine minefield to be laid in
the Carrick Roads, the battery was remodelled by 1898 to house two 6 pounder
quick-firing (QF) guns; the surviving concrete mounting and shell locker of
one gun is visible built into the western half of the battery's SSW flank; the
other gun position was in the angle between the south west and SSW flanks but
has been dismantled. These were complemented by a heavy machine gun whose
concrete-lined well, steps and mounting plinth survive in the angle between
the battery's SSW and SSE flanks. The guns were served by a new underground
magazine built of brick and concrete, situated beneath the battery and
accessed from a shaft, now capped, behind the gun positions. A recent
examination showed the shaft descends c.4.5m to a small lobby in whose western
side is a doorway to the brick-vaulted magazine measuring 4.46m east-west
by 2.62m north-south and up to 2.46m high internally.
This armament was soon inadequate and was withdrawn in 1903, having been
superseded by a much more powerful battery built between 1900 and 1904 on
high ground north of the Henrician castle and beyond this monument. That
battery also included three searchlight positions beside the coast, two of
which had been constructed in November 1896 to illuminate the minefield. A
further light was added during the construction of the 12 pounder battery
beyond this monument to the north west, but their power was provided from a
brick and concrete engine room within this monument, immediately beyond the
north west side bastion of the Henrician castle. The room adjoining the engine
room on the east side (currently used as a bothy by HPR) was the test room
which contained the (electric) batteries used to detonate the mines on the St
Mawes half of the minefield and in the friendly channel. The exit point of
the minefield cables can be seen on the rear wall. Its structure is protected
and largely masked by a thick turfed earth capping, leaving only its north
east and south east walls exposed. This became redundant with the closure of
the higher battery in 1910.
Re-fortification took place in 1941 when this monument became part of a more
extensive system of defences on the headland that formed St Mawes Battery in
World War II. The main armament, two 6 pounder guns, was sited beyond this
monument to the north west, but within the monument a Bofors anti-aircraft gun
was placed on the midslope terrace west of the Henrician castle. These guns
were assisted by four rock-camouflaged searchlights located on the shoreline
beyond the coastal revetment wall, extending as a row over 65m north west from
the Henrician blockhouse. The searchlights themselves have not survived but
the lower parts of their substantial rectangular emplacements remain, c.8m
long and 6m wide, built of rubble-faced concrete and aligned with their long
axes north-south. The earlier 1900-1910 engine room was reused to house the
dynamos powering the searchlights and the castle's guardhouse was used as a
store. The battery was operational until January 1945 and was finally closed
down and largely dismantled in 1956-7.
In all phases of its fortification, the command which this monument held over
the east side of the Carrick Roads complemented the control over the west side
operated by the more extensive defences on Pendennis Headland near the ports
of Falmouth and Penryn. Indeed the defences of the two sites developed very
much in tandem for most of the post-medieval period, supplemented by 1805 by a
battery on St Anthony's Head, to the SSE of this monument at the eastern
side of the entrance to the Carrick Roads.
All English Heritage notices, fixtures and fittings; the modern toilet block
and its base and the surfaces of all modern tracks 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

Artillery castles were constructed as strong stone defensive structures
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 of
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 are considered to be of national importance.

The Henrician artillery castle at St Mawes survives well, retaining a number
of original features rarely preserved such as the carved wooden door heads.
The castle is also unusual in its degree of decorative embellishment, a
feature which has set this monument apart in major reviews of this
fortification phase. The siting of this artillery castle and its nearby
blockhouse, together with their complementary association with surviving
contemporary defence works at Pendennis show well the defensive strategies and
capabilities deployed in the earlier 16th century. They demonstrate well the
intended aim of the overall defence policy under which they were constructed,
to deny harbours and anchorages to the enemy. The development of fortification
methods throughout the post-medieval period in the light of increasing
efficiency and range of armaments is clearly shown by the successive
modifications made within the monument. Again these are given a wider context
by their association with the surviving defences at Pendennis and, for later
periods, St Anthony's Head. The monument is also well documented throughout
its development, providing both the broad historical context and the detailed
background to its successive phases.

Source: Historic England


Books and journals
Carpenter, A C, The Cannon of Pendennis and St Mawes Castles, Cornwall, (1984)
Carpenter, A C, The Cannon of Pendennis and St Mawes Castles, Cornwall, (1984)
Cooper, R, A Teacher's Handbook to the Castles of Pendennis and St Mawes, (1994)
Cooper, R, A Teacher's Handbook to the Castles of Pendennis and St Mawes, (1994)
Cooper, R, A Teacher's Handbook to the Castles of Pendennis and St Mawes, (1994)
Dorman, J, The Later Defences of Falmouth 1895-1956, (1993)
Dorman, J, The Later Defences of Falmouth 1895-1956, (1993)
Heggie, A V, Lane, M, Delta Graphics, , St Anthony Battery
Johns, C, Pendennis Headland The Defences 1540-1956, (1992)
Johns, C, Pendennis Headland The Defences 1540-1956, (1992)
Morley, B, The Castles of Pendennis and St Mawes, (1988)
Morley, B, The Castles of Pendennis and St Mawes, (1988)
Morley, B, The Castles of Pendennis and St Mawes, (1988)
Morley, B M, Henry VIII and the Development of Coastal Defence, (1976)
Saunders, A D, Fortress Britain, (1989)
Stevenson, I V, Some West Country Defences, (1989), 11-26
Stevenson, I V, Some West Country Defences, (1989), 11-26
Stevenson, I V, Some West Country Defences, (1989), 11-26
Tosh, D, St Mawes Castle A Brief Guide, (1993)
Tosh, D, St Mawes Castle A Brief Guide, (1993)
DNH, Listed Building entry description for St Mawes Castle, 7/118,
DoE/HBMC, Ancient Monuments Terrier for CO 278, St Mawes Castle, (1984)
DoE/HBMC, Ancient Monuments Terrier for CO 278, St Mawes Castle, (1984)
Listed Building entry description for St Mawes Castle, 7/118,
Listed Building entry description for St Mawes Castle, 7/118,
MPBW Information Branch, Pendennis and St Mawes Castles, (1963)
MPBW Information Branch, Pendennis and St Mawes Castles, (1963)
Sharpe, A, St Mawes Castle: a small underground late 19th century magazine, 1990, Unpublished survey report for CAU/HPG
Sharpe, A/CAU, St Mawes Castle: a small underground late 19th century magazine, 1991, Unpublished CAU survey report for HPG
Title: 1:10000 Ordnance Survey Map; SW 83 SW
Source Date:

Title: 1:10000 Ordnance Survey Map; SW 83 SW
Source Date:

Title: Min of Wors plan and elevation of underground magazine, St Mawes
Source Date: 1920
MoW ref 97/14

Source: Historic England

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