Monument MPM15 - Southsea Castle

Henrician artillery castle built in 1544 to protect the approach channel to Portsmouth Harbour. The castle was restored to its 19th century appearance in the 1960s, and very few of the original Tudor features survive. Major changes to the design were carried out during the 17th and 19th centuries, and the castle continued to be used as a coastal battery until 1954. Evidence of the original Tudor structure was uncovered during groundworks in the courtyard and rooms on the western side of the castle in 2011. Two sections of the north-eastern edge of the Tudor castle's outer wall, together with early 19th century footings and brick sleeper walls, were revealed during a watching brief in the casements of the West Bailey toilets in 2021.

Built in 1544, this angle-bastioned fort with square keep protected the approach channel to Portsmouth Harbour. Much modified in 1814. Remained in military use until 1960, then taken over by City Council. [1]

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Henrician artillery castle built in 1544 which formed part of a network of fortifications to protect England's coastline. The castle was restored to its 19th century appearance in the 1960s, and very few of the original Tudor features survive. Major changes to the design were carried out during the 17th and 19th centuries, and the castle continued to be used as a coastal battery until 1954.

The castle was built in under six months in 1544 due to fears of an imminent French attack, and is said to have been designed by Henry VIII. The building work was overseen by Sir Anthony Knyvet. The original Tudor design comprised a small internal square keep, rectangular gun platforms to the east and west, and angled bastions on the north and south sides, surrounded by a dry moat. Henry VIII ordered several modifications after visiting in 1545, when he witnessed the sinking of the Mary Rose from the battlements. The Tudor castle has been extensively remodelled, but the majority of the exterior stone walls to the keep are the original Tudor construction. The Tudor well, which had been infilled during modifications of 1813-14, was re-excavated during restoration work in 1965 and is located against the north-east wall of the bailey. The line of the Tudor north curtain wall (demolished 1813-14) was revealed at the same time. Sections of what were thought to be the footings to the original north wall were also observed during work at the castle in 2011 (see below).

The keep was gutted by a fire in 1627, and the interior rebuilt several years later. In 1670 Charles IIs chief military engineer Sir Bernard de Gomme strengthened the defences by adding a new gun platform between the castle and the sea and constructing a glacis to protect the walls from artillery on the landward side. The gun platform was situated where the promenade to the south of the castle is today. Following de Gomme's redesign no further improvements were made for over a century, and the castle fell into disrepair. A large explosion triggered by gunpowder igniting in a storeroom caused extensive damage to the east wing in 1759.

In 1813 Major-General Benjamin Fisher, commander of the Royal Engineers in Portsmouth, was charged with the renovation of the castle which took place between 1813 and 1816. During this work a number of the surviving Tudor features were altered or demolished. The angled bastion facing the sea was remodelled to form a curved battery with magazines underneath. A counterscarp gallery was constructed in the outer wall of the moat with loopholes to provide flanking fire. This was linked to the castle by a caponier (covered passage). In order to accommodate extra troops barrack rooms were built on the east and west sides of the bailey, and the north curtain wall rebuilt 9m further north, creating space for extra rooms with a new gun platform above. The interior of the keep was modelled in red brick, and vaulted ceilings were added to strengthen it against enemy shells and the weight of guns on the roof. A Tudor watch tower on the roof of the keep was demolished and replaced by four gun positions. A new water supply in the form of a reservoir beneath the western bailey was added and the original well infilled. The pump to the reservoir can still be seen against the keep wall.

Between 1844 and 1850 the castle was used as a military prison, and the new barrack rooms converted accordingly. The bars on the windows of the keep date to this period.

New gun batteries were constructed to the east and west of the castle between 1863 and 1869 and the entire 17 acre site was enclosed by a high brick wall with loopholes to defend it against a landward attack. A remaining section of this wall can be seen in the D-Day Museum car park (see MPM936). The east battery was adapted between 1899 and 1901 to accommodate 6-inch breech-loading guns. In the years preceding the First World War the castle's role changed to that of range and direction finding for the east and west batteries.

During the First World War the castle was manned by members of the Royal Garrison Artillery and No. 4 (Portsmouth) Company of the Hampshire RGA Territorials, until this responsibility was taken over by the 'citizen artillerists' of the Hampshire RGA Volunteers in 1917. The castle became H.Q. Portsmouth Fixed Defences during the Second World War and was manned by the Hampshire Heavy Regiment R.A. (T.A). [4] The ATS and the Home Guard were also stationed at the castle during the war. At least two incendiary bombs hit the castle, but these caused limited damage.

The site was purchased by Portsmouth City Council in 1960 for use as a museum and restored to its 19th century appearance.

[2]

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Groundworks carried out in the courtyard and rooms on the western side of the castle in 2011 uncovered evidence of the original Tudor structure and later alterations.

Two sections of limestone rubble walls in a creamy white lime mortar observed in the courtyard and Room 24 were thought to form part of the footings to the original north wall, as shown on a Tudor plan of the castle. The wall in the courtyard was at least 0.70m wide by at least 200mm deep. The total depth was not established. Only the south-east side of this wall was exposed. The wall in Room 24 was 0.5m long by 0.75m wide, and the edges of the wall continued beyond the trench which had been excavated.

Two later red brick walls abutted the south-east and south-west sides of the Tudor wall in Room 24. These walls formed a right angle with each other, and were probably part of the same structure. They measured more than 0.38m long x 0.23m wide x 0.30m thick and more than 0.45m long x 0.23m wide x 0.07m thick respectively. The brick and limestone walls had all been sealed by a layer of very slightly stony, very dark brown, silty clay loam c75mm thick. The brick walls are not shown on any plans of the castle, and it has been suggested that they may represent unrecorded remodelling, possibly during the 18th century.

In the courtyard two further early-modern brick features were observed. Another brick wall, measuring at least 2.0m long x 0.50m wide with 60mm bricks in a pale yellow sandy lime mortar, was present in two trenches. A stepped square brick feature at least 700mm x 400mm x270mm and at least five courses high had been constructed using bricks 60mm thick and a hard white mortar. The alignment of this feature was at an angle to the walls of the rooms of the present castle. It was probably the base for a structural element.

Modern features comprised the base for a concrete layer, limestone slab paving in the courtyard and a concrete slab which formed the floor of Room 24.

[3]


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Two sections of the north-eastern edge of the Tudor castle's outer wall, together with early 19th century footings and brick sleeper walls, were revealed during a watching brief in the casements of the West Bailey toilets in 2021. Monitoring took place on trenches excavated in order to connect new toilets to existing sewer pipes situated under the casements' south-west walls.

The Tudor wall was revealed under the modern floor at a depth of 0.25m in the western casement and 0.3m in the eastern casement. Both sections of wall had been punctured by soil pipes, probably during renovation work carried out in the 1960s after the site was purchased by Portsmouth City Council. Only a small section of wall was revealed in the trench in the western casement. More of the wall was exposed in the trench in the eastern casement where the 1960s pipe had to be cut back. The wall was composed of undressed stone blocks bonded in a white mortar. Traces of a hard grey mortar render were found at its extreme eastern end, at which point it appeared to be turning to the north-east.

In both casements a stone footing which supported the brick casement walls above was butted up against the Tudor wall. This ran at right angles to the north-east of the wall, 0.25m below the existing floor in the western casement and 0.2m below in the eastern casement. It was made up of dressed stone blocks, which may have been robbed from the facing stones of the Tudor castle. The footing was thought to date to when the castle was re-modelled in the early 19th century. The base of the footings exceeded 0.9m in the eastern casement, which was excavated to a greater depth than the trench in the western casement.

Brick sleeper walls ran parallel to the stone footings. The walls were two courses deep and were found 0.3m below floor level in the western casement and 0.36m below in the eastern casement. It is thought the walls would have supported a suspended timber floor in each casement. The sleeper wall was bedded on a deposit of clean gravel, visible in the trench excavated in the eastern casement. The Tudor wall and 19th century footings had not been dug through the gravel. It has therefore been suggested that the casement walls may have been built up from the base of the Tudor ditch when the castle was enlarged in the early 19th century, and the space around them infilled with gravel up to the level of the sleeper walls of the casements suspended timber floors.

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Information about the outer construction of the counterscarp tunnels was recorded by Wessex Archaeology during the monitoring of geotechnical investigations in 2020. The tunnels formed part of extensive alterations at the castle carried out between 1813 and 1816, which included the remodelling of the seaward bastion and the construction of a counterscarp gallery linked to the castle by a caponier around the outer wall of the moat with loopholes to provide flanking fire.

The investigations suggested the brick lined tunnels were encased within a substantial masonry superstructure which includes the seaward side and roof. This is situated within redeposited storm beach deposits which are likely to form part of the basis of the redesigned sea defences which were constructed at the same time.

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The foundations of the caponier and interior castle walls within the moat were exposed and recorded during the monitoring of a test pit by Wessex Archaeology in 2023.

The caponier wall was constructed of smooth dressed limestone blocks between 0.30m and 1.40m long and 0.30m high arranged in uneven coursing. A single course of the wall lay below ground where it was bonded to a foundation. The wall butted against the interior castle wall. Evidence of modern restoration to some of the jointing was observed above ground.

The foundation of the caponier wall was encountered at a depth of 0.40m below ground level. It had been constructed using roughly dressed limestone blocks and extended an average of 0.20m beyond the outside of the caponier wall. The base of the foundation was not exposed but it continued to the bottom of the trench at 1.0m below ground level.

The remains of a layer of red clay up to 0.1m thick sealing the outside of the foundation and lower course of wall was thought to represent an attempt at waterproofing.

A 1.0m section of the interior castle wall was exposed where the caponier butted up against it. The wall had been constructed using smooth dressed limestone blocks between 0.44m and 1.0m long and 0.40m high arranged in uneven coursing. Only a single course of the wall lay below ground level where it was bonded to a foundation. Evidence of modern restoration to some of the jointing was observed above ground. The foundation was recorded 0.40m below ground level and was of the same construction as the caponier foundation. Both foundations were interpreted as belonging to a single phase of construction.

The backfill of the moat excavated within the 1.0m deep test pit dated to the 20th century. There was no evidence of any earlier phases of backfilling to this depth.

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Elements of former 17th and 19th century defences to the castle located within the area of the esplanade to the southeast of the castle walls were revealed during a watching brief on Sub-frontage 4 of the Southsea Coastal Defence Scheme. These comprised a wall to a former 17th century structure designed by Sir Bernard de Gomme [MPM2146], 19th century walls [MPM2147] and the remains of a 19th century gun emplacement located within the East Battery [MPM2148].

Part of the moat was also monitored during the works and it was observed that headstones had been used in the construction of the moat wall. The watching brief report suggests these may have come from Mile End Cemetery, the site of which was redeveoped in the 1970s [see MPM1584].

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<1> Portsmouth City Council, n/a, Portsmouth City SMR Cards, SZ69NW14 (Index). SPM1.

<2> Brooks, Stephen, 1996, Southsea Castle (Bibliographic reference). SPM387.

<3> Russel, J I & Elliott, G L, 2011, Archaeological Watching Brief at Southsea Castle, Southsea, Hampshire (Unpublished document). SPM386.

<4> Corney, A, 1967, Southsea Castle (Bibliographic reference). SPM390.

<5> West Sussex Archaeology, 2021, Report on an Archaeological Watching Brief at Southsea Castle, Clarence Esplanade, Southsea, Hampshire (Unpublished document). SPM584.

<6> Brennan, Naomi, 2021, Southsea Castle Portsea Island, Hampshire: GI Works Archaeological Watching Brief (Unpublished document). SPM642.

<7> McCarthy, Jamie, 2023, Southsea Coastal Defence Scheme, Sub-Frontage 4, Southsea Castle: Archaeological Watching Brief - Caponier Investigation (Unpublished document). SPM644.

<8> Williams, Rachel, 2025, Southsea Coastal Defence Scheme Sub-frontage 4, Southsea Castle, Southsea, Hampshire: Archaeological Watching Brief (Unpublished document). SPM671.