Calshot Castle: a 16th century artillery castle


Heritage Category:
Scheduled Monument
List Entry Number:
Date first listed:
Date of most recent amendment:


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The building or site itself may lie within the boundary of more than one authority.

New Forest (District Authority)
National Park:
National Grid Reference:
SU 48880 02490

Reasons for Designation

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.


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.


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

Legacy System number:
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Books and journals
Coad, JG, Calshot Castle, (1991)


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.

End of official listing

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