Monument MPM387 - Town Mount Bastion

Site of the Town Mount Bastion. Part of the former line of fortifications that protected the town of Portsmouth, the Mount defended the Town Gate at the northern end of the High Street, and was in existance by the Tudor period. During the 17th century it was incorporated into the new line of defences designed by De Gomme in the 1660s. The defences were extensively remodelled by Demaretz during the mid-18th century. The bastion was demolished during the c1860s/1870s.

The Town Mount Bastion, sometimes refered to as 'The Great Bastillion', was in existance by the Tudor period and appears on 16th century maps of Portsmouth. Originally an earthwork, it defended the Town Gate at the northern end of the High Street, which controlled access to the road to london. It had been enlarged by 1568, and is thought to have been the first example of an Orillion type bastion in England. When visiting Portsmouth in the 1560s, John Leland described the Town Gate and Mount as 'a gate of tymber at the North East Ende of the Town and by it is cast up an hille of erth diched wherein be gunnes to defend entre into the town by land'. During the 17th century the Mount was incorporated into the new defences designed by De Gomme in the 1660s. The defences were remodelled again by Demaretz during the mid-18th century. The town defences were demolished during the c1860s/1870s.

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A watching brief undertaken on the site of the former Students Union in 2004, revealed the remains of what was thought to be part of the forward facing wall of the east side of the Town Mount Bastion (located at approximately SZ63609964 and SZ63619961).

Two sections of massive stone walls were uncovered in trenches (running north-south) in the western half of the site. One section of wall was 2.8m thick and bonded with lime mortar. It had been faced with limestone on its south side, and had a coarse, possibly destroyed, face on its north. The second section of wall was constructed from limestone, over 2m thick, with stone facing on its south face. It survived in three parts, possibly resulting from variable demolition. The north face had been partly destroyed, and a dump of foundation rubble was found to the north of the wall. Beyond the walls would have been a moat. The only evidence found during the work that possibly related to this feature were two gravel layers, which may have resulted from the infilling of the moat. As the backs of both of these walls (west side) retained their facing blocks, while the east sides had been destroyed, it is possible that the latter had been pulled into the moat.

Accession number: 2004/962

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An archaeological evaluation in Ravelin Park in 1972 revealed the remains of part of the north facing wall to Town Mount Bastion, the moat that surrounded it and part of the counterscarp wall. See MPM1878 for details.

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The remains of Town Mount Bastion and moat were observed during archaeological investigations in 2018-2019.


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 was 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 trampled during the demolition process. This contained 19th century finds including an 1860 penny.

The scarp wall had subsided slightly after the demolition, a grey void filled by accumulated greyish brown silt.

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 for clearance and infilling. An 1860 penny, 1861 halfpenny and navy 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.


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<1> Patterson, B.H., 1987, A Military Heritage A History of Portsmouth & Portsea Town Fortifications (Bibliographic reference). SPM43.

<2> Currie, C K, 2004, An Archaeological Watching Brief at the Old Student Union Site, Ravelin Park, Museum Road, Portsmouth, Hants (Unpublished document). SPM116.

<3> Fox, Russ, 1988, East Ravelin (Excavation archive). SPM12.

<4> Anthony, Sian and Capon, Les, 2019, University of Portsmouth Sports Building, Ravelin Park, Portsmouth, Hampshire: Post-Excavation Assessment Report (Unpublished document). SPM593.