Details

The monument includes Calshot Castle, a mid 16th century stone built artillery
castle with 18th and 19th century alterations, lying on Calshot Spit on the
southern shore of Southampton Water.
The precise and symmetrical plan of the castle centres on a three storey gun
tower or keep, separated from the surrounding curtain wall by a courtyard
within which lie both accommodation buildings and later searchlight
emplacements. The buildings of the castle are surrounded by a shallow
stone-lined moat beyond which, on the seaward side, lie a stone-paved
counterscarp and stone sea defences. The keep is approximately 16m in external
diameter, but only 8m internally. The lower storey is octagonal in plan, but
the upper two floors, while retaining an octagonal interior plan, are
cylindrical on the outside. The external appearance of the upper part of the
tower differs from the original only in having the parapet on the roof altered
in the 18th century and concrete gun emplacements added in 1907. The 18th
century alterations involved the replacement of the curved parapets with their
embrasures for heavy guns with an unbroken parapet designed to protect troops.
In 1907 the parapet was further modified on its east side by the addition of
mass concrete to form emplacements for two 12 pounder guns.
Internally the keep is divided into three levels below the roof. The basement
may originally have been vaulted although, due to considerable alterations,
little is known of its original form. In 1896 the installation of generators
and other equipment for Defence Electric Lights (searchlights) necessitated
the construction of a protective concrete ceiling. The basement was lined with
brick and possibly deepened at this time while new access was provided from
courtyard level. That from the first floor was blocked. In 1907 the generators
were removed and the basement was converted to a cartridge and shell magazine
by the insertion of a brick cross wall with lamp niches and an ammunition
hoist, now removed.
The modification of the basement ceiling resulted in the floor level of the
first floor being lowered by 2 feet (0.6m). At this time the first floor,
which retains its 16th century outline and the remains of an original
fireplace, was converted to a barrack room. The second floor has also been
considerably altered, although its walls are largely Tudor and incorporate the
remains of two fireplaces and a garderobe. This level once carried heavy guns
firing through large embrasures but was also converted into a barrack room in
the late 19th century. The ceiling was subsequently strengthened to help
support the newly installed roof battery. Traces of the ammunition hoist which
ran from the basement to the roof can be seen in all floors and ceilings
throughout the keep.
The courtyard is enclosed by a 16-sided curtain wall with a flared apron
sloping into the moat. Formerly 15 of the sides possessed embrasures
through which the courtyard guns fired and above which was a deep parapet
shielding the wall walk behind. The 16th side was occupied by the gatehouse.
In c.1770 the majority of the curtain wall was lowered to its present height
and the gatehouse was extended, preserving the original embrasures on either
side of the entrance. On the north side of the courtyard is a long concrete
building constructed c.1896 to hold three searchlights (Defence Electric
Lights). Three of the Tudor embrasures were cut back at this time to provide a
better arc for the searchlights and a further embrasure is blocked to each
side of the three.
The gatehouse in its original form is shown by an early 18th century engraving
to have been a simple two storey structure, probably with a single room above
the gate passage. The gatehouse was flanked by a gun embrasure at first floor
level on its western side and its roof also had provision for guns. The gate
passage is approached from over the moat by a 19th century fixed metal-framed
bridge; a replacement for the wooden structure shown on early 18th century
engravings. The grooves for the portcullis which originally protected the gate
passage can still be seen. In c.1770 the gatehouse was heightened and widened
to provide better accommodation for the governor. The section added to the top
of the original gatehouse has one small window while the flanking additions
have none. The accommodation thus provided has been extensively altered
internally. Alterations carried out in 1896 included the provision of a
guardroom and cell on the west side of the gate together with the construction
of a brick cookhouse, storerooms and latrines on the south end of the
gatehouse.
The stone-lined moat which lies beyond the curtain wall is 16-sided, 2.6 deep
and 8.8m wide. Beyond the moat on the seaward side, to the north, east and
south east, is a counterscarp, paved with stone and gently-sloping. Stone sea
defences are also provided on the east side of the castle. The precise extent
of these features is uncertain as they are now buried by shingle
accumulations.
Calshot Castle was constructed as part of a chain of coastal fortifications
built to protect vulnerable points in the event of a French invasion. Calshot
Spit dominates the shipping route to Southampton as the deep water channel
runs close to shore at this point. The major construction work was carried out
in 1539 and 1540, most probably using building stone from Netley or Beaulieu
Abbey. Documentary evidence records that the lead for the roof came from
Beaulieu. By the end of the 1540s Calshot was one of the most heavily armed of
the Solent fortresses, with a total of 36 guns, though this had fallen to ten
serviceable guns by 1559. In 1584 Queen Elizabeth's government devoted funds
to the repair of several of the Solent defences as part of its precautions
against a possible invasion from Spain or the Netherlands. Calshot by this
time had suffered a disastrous fire which had gutted the keep and timber
repairs required 127 trees from the New Forest.
The strategic importance of Calshot ensured its survival during the Civil War
when neighbouring castles at St Andrew's and Netley were disabled. During the
War of Spanish Succession (1702-13) it was equipped with a maximum of 25 guns
but this was reduced to 13 by 1725. The first significant alteration of the
Tudor fabric, which took place in 1774, preceded several complaints about old
and defective guns.
In the late 19th century searchlights, or Defence Electric Lights, were
installed at Calshot to be used in conjunction with a quick fire gun battery
which was built to the south east of the castle and completed in 1897. Nothing
now survives of this battery and it has not been included within the
scheduling. Generators powered by oil engines were installed in the basement
of the keep while the two floors above resumed their role as barrack
accommodation. The interior of the gatehouse was extensively altered between
September 1896 and November 1896.
In 1907 Calshot Castle underwent its last major modification as a fortress.
The roof of the keep was strengthened to permit the installation of a pair of
quick fire guns to augment the adjacent battery. The searchlight generators
were removed from the basement which was converted to a cartridge and shell
store, linked to the roof by a hoist in the centre of the keep.
Calshot and its adjacent battery were stripped of their weapons before the end
of the World War I. However, in 1940, two quick fire guns were remounted on
the roof of the castle and six searchlights installed. In its final period of
active service, Calshot Castle, together with Bungalow Battery on the north
shore of Southampton Water and Stone Point Battery some 3 miles to the south
west, formed part of Calshot Fire Command. In 1953 Calshot air station was
transferred to Maintenance Command before finally being closed.
Calshot Castle is Listed Grade II* and is in the care of the Secretary
of State.
Excluded from the scheduling are all recent fixtures and fittings for shop,
exhibition and accommodation; also excluded are all floodlights, guns, signs,
concrete anchor blocks and the reproduction furnishings within the two barrack
rooms, although the ground beneath all of these features is included.

MAP EXTRACT
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.

Calshot Castle is a well preserved example of its class within which, despite
later alterations, all elements of the original structure have survived in a
recognisable form. The alterations, carried out from the 18th century onwards,
demonstrate the continuing importance of Calshot in the defence of Southampton
Water over a period of 400 years. Situated in a prominent position on Calshot
Spit the castle is an important landmark and is open to the public.

Source: Historic England

Sources

Books and journals
Coad, JG, Calshot Castle, (1991)

Source: Historic England