Monument MPM2033 - Remains of post-medieval town defences, University of Portsmouth Sports Building, Ravelin Park

The remains of the former post-medieval defences comprising Town Mount Bastion, the counterscarp, moat and East Ravelin were observed during archaeological investigations ahead of the construction of the University of Portsmouth Sports Building in Ravelin Park in 2018-2019. The defences formed part of the Portsmouth Line of fortifications surrounding the town that were constructed in the late-17th century by Sir Bernard de Gomme, and later remodelled by Peter Desmaretz during 18th century. The defences were demolished in the 1860s/1870s.

See records MPM387 and MPM1877 and MPM1878 for further information and remains recorded during previous investigations for Town Mount Bastion and records MPM34 and MPM1879 - MPM1882 for the East Ravelin.


Town mount Bastion
The scarp (inner side of the moat) was supported by a limestone wall forming part of Town Mount Bastion which would have created a near-vertical rampart. The counterscarp (outer side of the moat) was constructed using a stone wall. A 40° glacis (slope) extended from the counterscarp to the rear of the East Ravelin.

A wide construction cut suggested that the excavation of the moat and construction of Town Mount Bastion had taken place at the same time. On the western side of the bastion wall this cut had been infilled with deposits upcast during the excavation of the moat which had probably been used to form the mount base of the bastion. This deposit appeared to have been reworked at a later date as it contained a clay tobacco pipe bowl dating to 1690-1700.

The bastion wall had been constructed using roughly coursed limestone blocks with a rubble core and survived to a maximum height of 4.06mOD (3.61m above the base of the moat). The base of the wall was not observed. It measured 1.60m wide at the uppermost surviving level with a 4° batter (slope) on the moat-facing side.

The wall was faced with blocks measuring 0.71m by 0.42m by 0.24m, although smaller blocks had also been used. Thinner limestone slabs 0.06m thick were observed in the west face of the wall where they had been used to provide a level bed for higher courses. Medium blocks of blue lias had also been used occasionally within the construction of the wall. Three rectangular blocks measuring 0.18m wide and 0.34m high set vertically at different levels had probably been used to fill putlog holes. A layer of slate laid at 2.72mOD may have been used as a damp course, suggesting there was a high water level in the moat.

The scarp (inner wall of the moat) had been modified at a later date with the addition of gun embrasures for canon which overlooked the moat. These were represented by a series of short regularly-spaced limestone walls on the inside of the scarp. A total of nine gun embrasures were recorded during the investigations.

The watching brief revealed the full extent of Town Mount Bastion which was recorded for a length of 40m with no changes of orientation.



Counterscarp
The counterscarp was situated 24m east of the bastion (scarp) wall and had been faced with stone revetment.

The counterscarp wall had been constructed using limestone blocks 0.55m by 0.32m by 0.24m which were bonded with lime mortar. It ran on a north-south alignment parallel with the bastion (scarp) wall. The wall measured 0.90m wide and was supported by five slightly irregularly spaced buttresses 0.90m by 0.90m positioned approximately 2.90m apart. The facing stones had been robbed from the western face of the counterscarp wall (that facing the moat) but the eastern side of the wall had survived undamaged below the level at which it had been demolished.

The wall survived for a length of 27m within the area covered by the watching brief. When the defences were demolished in the late 19th century the wall had been reduced to 2.92mOD.

The counterscarp turned east for 49m and beyond the area covered by the watching brief. The wall was constructed from squared limestone blocks 0.50m by 0.42m by 0.30m and was well coursed and bonded with sandy lime mortar. Buttresses had not been used to support this section of wall. The construction cut had been backfilled with friable mottled yellowish-brown silty clay. The wall had been reduced to 2.92mOD when it was demolished.

It has been suggested this section of the counterscarp may have been a secondary part of the defences after de Gomme's redun had been remodelled to form the East Ravelin.


Demolition
The bastion wall had been demolished to 4.06mOD and the outer side robbed of its faced limestone to a level of 2.72mOD. The depth of the demolition had probably been limited by the water level in the moat preventing access to the lower levels, as the backfill of the moat overlaid the demolition horizon. A compact layer of greyish brown sandy clay silt on the outer moat side of the scarp represented a layer that had been trampled during the demolition process. This contained 19th century finds including an 1860 penny. The scarp wall had subsided slightly after the demolition.

Thirty layers of infill were identified in the moat. The first, and one of the most substantial, was a layer of dark brown sandy silt containing gravel inclusions and occasional limestone rubble which overlay the remains of the scarp. This deposit was overlain by a series of layers ranging from yellowish brown to dark brown with varying gravel content. At the end of this sequence was a clean layer of brown silty sand and gravel which may have represented a redeposited geological horizon or a change in the location of material used for clearance and infilling. An 1860 penny, 1861 halfpenny and naval officers brass button were recovered from this deposit. The next layer of infill was stony and contained a mid-18th century clay tobacco pipe decorated with the Prince of Wales feathers. This deposit had been sealed by a particularly dark brown layer, which may originally have been topsoil or household dump due to it's organic character, or may have related to a period when the site was unused prior to final levelling. Finds recovered from this layer included a lead musket ball, clay tobacco pipe dating to 1640-1660 and 17th century pottery. The sequence continued with further layers of sandy clay gravel, the final fill lying closer to the ravelin, suggesting the moat had been infilled from this direction.



East Ravelin
The northern and inner walls of the East Ravelin together with part of the moat were observed during the investigations.

The northern wall was constructed of faced limestone blocks 0.48m by 0.40m by 0.30m with a rubble core. The wall survived to a height of 3.33m and was observed for a length of 25m, continuing beyond the limit of the excavations. Four gun embrasures for cannon were identified on the inner side of the wall overlooking the moat along the line of the scarp. Two of the embrasures were recorded in detail. These were 0.95m long forming an opening 2.60m wide over the scarp and splayed to 3.80m wide at the rear. They were the same size as the embrasures added to Town Mount Bastion (see above) indicating that the embrasures on the bastion were also added by de Gomme. The inner face of the wall was backfilled with clay which may have strengthened the wall through waterproofing and resilience.

The moat around the ravelin was 16.48m wide, it's base was not observed during the excavations. The moat cut was effectively also the construction cut for the ravelin wall on the north side.

The inner wall of the ravelin was constructed of limestone and 10% yellow sandstone. It measured 1.50m wide and survived to a maximum height of 3.56m OD. The base was observed as going to 0.30m OD. The remains of the wall consisted of four courses of foundation, the largest blocks measuring 0.50m by 0.40m by 0.12m. The stone had been bonded with coarse lime mortar that included small grits and charcoal in its make-up. The wall was recorded for a length of 26m. An integral brick drain led from the east side of the wall into a ditch-like channel cut into the glacis of the ravelin. The bricks were of varying sizes, possibly having been re-used. A sample of the drain's dark brown clayey silt fill contained tiny inclusions of building material and black grit of a possible industrial source.

The drain fed into a ditch 0.78m wide and 0.85m deep with a steep western edge and uneven base. The ditch ran parallel to the wall and was filled with a series of deposits of domestic origin. These were thought to probably represent items used upon the ravelin during it's final years. A large assemblage of residual fragments of pottery and glass dating to the 19th century and earlier was recovered from the lowest fill of the ditch, a layer of coarse black grit. The pottery included earthenwares, porcelain, tablewares, including a broken teacup and saucer, and stoneware jars. A glass drug bottle from a chemists in Palmerston Road, Southsea, was recovered from a layer of clean brown silt up to 0.21m deep immediately above. This was overlain by a second deposit of black grit up to 0.16m deep. A sample of this layer contained bottle glass, coal, clinker and oak charcoal fragments. The top fill of the ditch was mottled brown silty clay which lay slightly lower than the demolished wall. A clay tobacco pipe dating to 1760-1800 was recovered from the fill, together with residual 16th-17th century pottery and 19th century bottle glass.

A layer of organic clayey silt at the base of the ravelin moat was thought to have accumulated when the moat was in use. A sample of this deposit contained charcoal, clinker and coal fragments and a small glass bead. A Mesolithic flint core and a small sherd from a 14th century jug were also recovered from the deposit. Further investigation was limited by groundwater. This deposit was overlain by a layer of brown clayey silt which represented the first backfilling of the moat. This contained part of a 17th century Verwood-type jug, 16th century brick fragments and animal bones from cattle, sheep, horse and red deer. The second fill was a patchy dump of reddish brown sandy clay. Above this were a sequence of dumped deposits relating to secondary infilling which appears to have been added from outside the defences. The next sequence were added from the ravelin itself. A stony fill at the top of the moat resembled local sand and gravel and probably represented disturbed geological deposits used as the final levelling fill. Fragments of 18th century 'onion' bottles were collected from the dumped deposits.


19th - 21st Century

A small elongated pit 1.8m long by 0.51m wide by 0.17m deep lay directly against the internal face of the counterscarp wall. The pit had been filled with mid-grey brown silty clay and moderately large fragments of red brick with lime mortar. This may have been a robber cut to remove stone from the fortifications for re-use during the 19th century demolition works or it may date to slightly after.
Two intercutting pits found within the construction cut of the counterscarp wall post-dated the walls construction. The features may have been associated with the demolition of the defences or be slightly earlier in date. These comprised a pit/small linear feature 1.04m wide by 2.10m long and 0.45m deep filled with a silty clay which had fine gravel inclusions, oyster shell and fragments of clay tobacco pipe which had been heavily truncated by an ovoid pit 1.30m wide by 2.10m long by 0.40m deep filled with silty clay with moderate gravels and limestone fragments.

The counterscarp wall had been used as a base for a concrete foundation to the Second World War NAAFI (Navy, Army and Forces Institute) building that stood in the south-west corner of Ravelin Park. The foundation was 0.30m deep with bricks manufactured by Southwater. The NAAFI building was later used as a Student's Union and was demolished in 2004, after which the site became a university car park.

Other features associated with the NAFFI included a salt-glazed sewer pipe within a trench and a drain with a rubble fill. A demolition deposit of brown silty clay with occasional limestone fragments was found over the inner/western wall of the ravelin.

The demolition of the NAFFI building was represented by a widespread layer of rubble which included bricks manufactured by Warnham SB Co of Sussex. This deposit had been cut by modern services. Services had also cut through the ravelin embrasures and a small section of the western ravelin wall (0.5m by 0.3m and 0.5m deep) had been taken out and tipped over when the services were constructed.

A layer relating to the sites former use as a car park during the early 21st century overlay the demolition deposits. This included mixed hardcore overlain by tarmac painted with car-parking spaces.


Accession No: 2018/36

Anthony, Sian and Capon, Les, 2019, University of Portsmouth Sports Building, Ravelin Park, Portsmouth, Hampshire: Post-Excavation Assessment Report (Unpublished document). SPM593.