Monument MPM206 - Hilsea Lines

Fortified line of defences on the northern shore of Portsea Island. The first Hilsea Lines were constructed during the 1750s to designs by Desmaretz, who had been given the task of improving Portsmouth's fortifications. Following years of neglect the earlier defences were demolished during the mid-19th century when the present Lines were built to the specifications of Assistant Inspector General of Fortifications, Colonel Jervois. They were completed in 1870, although some later additions were made.

The Hilsea Lines were constructed between 1858 and 1871 and were the last of a series of fortifications built at the northern end of Portsea Island, protecting the land approaches to the Portsmouth dockyards from the north. The defence of Portsea Island is believed to have originated with a fortification (the Portway bulwark) erected in the reign of Henry VIII on the north bank of Port (or Portsbridge) Creek to protect its bridge. A fortification on the site was defended by Royalist forces in 1642 during the Civil War. At the Restoration, under Charles II, the Dutch military engineer, Bernard de Gomme (1620-1685) began the reconstruction of Portsmouth’s fortifications and plans show the fort defending the bridge, dated 1660 and 1666. In 1688 under Martin Beckman (1634/5-1702), the fortification at the Port Creek crossing was rebuilt. In the C18, with the abandonment of de Gomme’s fortifications around Portsmouth itself in 1730 and the increased development of Portsea, there was a need for new and stronger fortifications at the north end of the island. Between 1756 and 1757 defensive lines were constructed by John Peter Desmaretz (c1686-1768), Clerk to the Fortifications for the Portsmouth Dockyard. He was also responsible for building the Gosport Lines on the other side of Portsmouth harbour around the same time. The Hilsea Lines ran along the south bank of Port Creek (with an outwork on the north bank guarding the bridge, which had been rebuilt again in 1746). The Lines consisted of an irregular zigzag trace with three principal batteries and a single magazine. It had a 4.6m to 6m wide, 2m deep, ditch and a 2m to 2.4m earth rampart. Apart from the addition of a new work known as the Hilsea Redoubt, incorporated into the Lines when they were pierced by a railway line in 1846, and the addition of four expense magazines in 1853, the lines remained largely unchanged for 100 years.

By the late-1850s a combination of endemic mistrust of France and resultant fear of a potential invasion, developments in military technology, lessons learned from the siege of Sebastopol during the Crimean War, and criticism regarding the poor state of Portsmouth’s defences, lead to calls for a review of the dockyard’s fortifications. Consequently in 1857 Colonel WFD Jervois (1821-1897) of the Royal Engineers submitted plans for ’completing the defence works of Portsmouth’. This concluded that existing defences were too close to the dockyard, were too small and had fields of fire masked by buildings erected outside the lines. The Hilsea Lines themselves were considered to be ‘of weak trace and low profile’ and it was proposed, along with recommendations for other improvements for the overall defence of Portsmouth and Gosport, that they be reconstructed. Work on the Hilsea Lines and Gosport forts began in 1858. In addition to the rebuilding, batteries on Horsea Island and Shut Point to protect the flanks of the Lines and a further work on Pewitt Island to link the Portchester and Gosport lines were proposed. The design for the new Lines consisted of a bastioned trace on the south bank of Port Creek consisting of earth ramparts fronted by a water-filled ditch with three full bastions and two demi-bastions equipped with brick Haxo casemates, housing ten and five guns respectively (apart from the eastern flank of the East Bastion and the East Demi-Bastion which, considered less liable to attack, were not to have casemates). On the north bank were three outworks, the outer two of which protected the road (which was repositioned) and railway bridges. These were later linked in revised plans. Two small forts to the rear of the Lines were included in the plans but never built. Port Creek was straightened, widened and deepened, with dams added at either end to make it non-tidal.

Approval for the construction of the new Lines was obtained in January 1858 and William Piper of London, was awarded the first contract for the demolition of the old lines and the building of the casemates and the entrance gateways. By 1859, however, the development of the Armstrong rifled breech-loading gun with increased accuracy and range led Jervois to rethink his proposals fearing that a force which occupied Portsdown Hill could now bombard the dockyard and Lines from long range. He proposed that the Hilea Lines be abandoned and that a new line built on top of Portsdown Hill. This was rejected by a committee chaired by the Duke of Cambridge, Commander-in-Chief of the army, who whilst agreeing that a fort of Portdown Hill was required, considered that the Hilsea Lines should be retained as a physical barrier to the occupation of Portsea Island from the landward side. In the meantime, the launch of the French ironclad ‘Gloire’ and the strengthening of their navy caused a new invasion scare and obliged the government to appoint a Royal Commission to review the defence of the country and, in particular, that of the naval dockyards. This resulted in the construction of some 70 forts and batteries in England, including the Spithead and Portdown forts, which collectively became known colloquially as 'Palmerston's Follies' after Lord Palmerston (1784-1865), who was Prime Minister at the time.

The commissioners had supported the retention of the Hilsea Lines, but made a number of amendments to Jervois' original plans. The island flanking works and two rear forts were omitted and the west of the lines, which had extended southward opposite Horsea Island, truncated. The outworks on the north bank of Port Creek were also never built. The initial construction contract had been completed by March 1861 but, partly due to problems with subsequent contractors the works were not completed until 1871. However, in line with the Royal Commission forts, the Lines did not receive their armament until 1886 by which time they were already considered largely obsolete. The original armament had been intended to comprise 168, 32lb smooth-bore muzzle-loading (SBML) guns on the terreplein and 50, 64lb SBML guns in the casemates. This was overtaken by the advances in artillery technology and they were probably never installed. In 1886 the Lines were equipped with a mix of three 7-inch rifled muzzle-loading (RML) and three 7-inch Armstrong rifled breech-loading (RBL) guns, on ‘pop-up’ counterweighted Mark II Moncrieff mountings in newly installed concrete gun pits on the bastions. Additionally, twenty 7-inch RBLs were mounted in the casemates along with moveable armament of eight 40lb RMLs and four 6.6-inch howitzers on travelling carriages. All armament was removed in 1903. During the First World War a small number of anti-aircraft and other guns were mounted on the terreplein.

In 1919 the main gateway of the Lines, consisting of two vehicular and a pedestrian tunnel, was demolished to allow for road widening, followed in 1932 by a bus depot resulting in the demolition of the battery to the west of the gate. The West Demi-Bastion was converted into changing rooms for Portsmouth Grammar School. Also in 1932, the East Demi-Bastion, East Curtain and part of the East Bastion (including two of the six Moncrieff gun pits) were demolished to make way for Portsmouth aerodrome. In 1933 the western end of the moat was turned into a boating lake and lido.

During the Second World War a number of obsolete anti-aircraft guns were installed and the Lines were manned by the Home Guard. Some of the magazines were used as air-raid shelters and at least one pillbox was built on the ramparts. In 1940 a cutting was made through the Lines to access a new causeway across the Port Creek at the eastern corner of the West Bastion.

In 1986 the council purchased the remainder of the Lines and laid out parkland and walks on much of the north side of the lines. Most of the ramparts, especially at their eastern end, are, at the time of writing (2020), heavily overgrown with largely impassable footpaths (except at the west end of the Lines). A number of the casemates are in commercial use and the Portsmouth Grammar School owns the West Demi-Bastion (Bastion One) with the land behind used as their playing fields.

[1]



Several features relating to modifications to the interior of the casement were revealed during a watching brief at Bastion 4 in 2006, including the blocking of the casement arch, and the remains of earlier internal walls. A small ditch which may have been related to the 18th century earthwork ramparts, and a water tank were also recorded on the site.

The later blocking up of the casement arch may have been represented by a wall (1) on a northeast-southwest alignment, which extended to the full height of the arch and had a small central doorway. Below the base of the wall, on the same alignement, were two courses of bricks (5), one of headers laid on edge above a course of strechers. This may have been the base of an original/earlier phase of walling across the casement arch. It was separarted from wall 1 by a thick layer of mortar, and therefore wall 1 was probably a separate, later, phase of building.

A linear brick feature (4)on a southeast-northwest alignement, and a deposit of rubble found below the modern concete, would suggest that the interior of the casement had been modified at some point, probably during the 20th century. The brick feature may have been part of a former internal wall within the casement that had been removed.

Roughly parallel with the rampart was a feature (10) with a V-shaped profile. It measured c. 530mm w by c. 450mm deep, and was possibly a small ditch related to the construction of the 18th century earthwork ramparts.

A rectangular sunken feature (15), the full extent of which was not exposed, was probably a water tank. It measured 2m eastwest and northsouth, and its fill was made up of recently deposited modern rubble and debris.

[2]


An historic building recording of Casemate 5 at Bastion 3 of Hilsea Lines was carried out by Wessex Archaeology in 2023 ahead of proposed renovation works to replace the existing floorboards and to clean a corrugated metal percussion screen (blast shield). The results are summarised below, but the report should be consulted for the full details of the survey.

The brick-built casemate is a roughly square chamber with a barrel-vaulted ceiling and concave east wall, the upper part of which incorporates a blast shield to protect from a gun gallery on the other side of the wall. The interior measures 5.18m long north-south by 4.73m-5m wide (allowing for the curved east wall) and a maximum of 3.78m high. Remnants of limewash were observed on the walls and ceiling and the remains of a brick fireplace with an iron hearth were located on the south side of the room. Remnants of black paint on the walls around the fireplace suggested there had originally been a chimneypiece. The fireplace is shown on a plan as having stood back-to-back with another in casemate 6. Two pairs of iron coat hooks and shelving racks had been fitted to the walls on the north and south sides of the room, two of the racks were intact.

The floor had been constructed using regular timber floorboards nailed onto joists embedded in a layer of bituminous (or asphalt) infill material. Thin pieces of timber ‘stripwood’ had been laid under the joins in the floorboards and may have been glued in place. The floorboards were fixed to the joists by pairs of spur-headed cut nails aligned in rows. The edges of the floor were held down by an iron band with fixing points (possibly screws) at various intervals. It was noted that other renovated casemates in Bastion 3 had sprung timber floors and casemate 3 had a flag stone floor. The bitumin-like infill in casemate 5 may have been an original feature, but was thought more likely to have been a later modification with the use of bitumen and asphalt in flooring becoming much more common during the late 19th and early 20th century. It may have been used as damp-proofing or to protect against vermin/insect infestation. It was not possible to see what lay beneath the bitumin-like material as it was retained as part of the renovation work.

It has been suggested that casemate 5 may have been used as a kitchen due to the use of the bitumin-like infill in the flooring. However, the fireplace, coat hooks and shelving racks suggested the casemate was used as a barrack room/accommodation with the bitumin being added to the flooring as a later modification.

[3]

Portsmouth City Council, n/a, Portsmouth City SMR Cards, SU60SE30 (Index). SPM1.

<1> Historic England, The National Heritage List for England (Index). SPM35.

<2> Cottrell, P R, 2006, Archaeological Watching Brief at Bastion 4, Hilsea Lines, Scott Road, Hilsea, Portsmouth (Unpublished document). SPM166.

<3> Flood, Grace, 2023, Casemate at Bastion 3, Hilsea Lines, Portsmouth: Historic Building Record (Unpublished document). SPM679.