Monument MPM2008 - 18th century fortifications, University of Portsmouth, North Campus

A section of curtain wall reinforced by five buttresses and part of the ditch/dry moat to the late 18th century Portsea line of fortifications recorded during a watching brief in 2007.

A section of curtain/escarp wall reinforced by five buttresses and part of the ditch/dry moat to the late 18th century Portsea line of fortifications was observed during a watching brief by Southampton Archaeology Unit in 2007. The section of wall was shown on plans to have been situated between the Townshend Bastion and the Right Demi Bastion to the fortifications. The observations were made during groundworks for Building 1 at the University of Portsmouth's North Campus in Lion Terrace.

The curtain/escarp wall had been constructed using limestone rubble bonded with lime mortar. The wall had been built within a substantial foundation trench, the western edge of which curved around buttresses built against the inner western face of the curtain wall (see below).

The surviving section of wall was c2m wide at the top. The east outer face sloped steeply outwards and was c2.75m wide at a depth of 4m. The facing stone had probably been robbed when the defences were demolished as the face on this side was rough and uneven. The west face was near vertical and had been faced with roughly dressed blocks. A stepped footing was recorded 3.1m beneath the top of the wall on the west side, adjacent to a buttress. The base of the wall was recorded at c4.5m below the top by one buttress and 5.5m between two further buttresses.

A total of five buttresses were exposed, which had been built against the inner western face of the curtain wall to strengthen it. These had also been constructed using limestone rubble bonded with lime mortar. The sides and rear faces were vertical and they had been faced with roughly dressed rectangular stone blocks. The base of one buttress was observed 3.6m below the top.

The buttresses were tapered in plan. Where they joined the wall they were c1.8m wide and the western ends c0.9m wide. The lengths of the buttresses varied between c2.4m and c2.65, and the spacing between them 3.55m - 3.9m.

The curtain wall and buttresses had been constructed on a foundation of bricks and horizontal timbers observed beneath them. The foundation consisted of bricks laid flat in two or three courses, probably bonded with lime mortar, and a series of timbers which had been laid on top of the bricks beneath the stone wall. The timbers had been laid longitudinally on the alignment of the wall between the buttresses in one section and at 90o to the wall alignment in others. In one area beneath one of the buttresses there were no bricks. In another the timbers extended east of the surviving face of the wall.

Further timbers were recorded, some of which may have originally been fastened to the horizontal timbers. These included vertical timbers observed at the outer face of the wall.

The ditch/dry moat was recorded to the east of the curtain wall. The spoil from the ditch would have been banked up against the west side of the wall to form the rampart. The wet moat would have been situated beyond the extent of the excavated area, and was not encountered during the watching brief.

Limestone fragments and blocks and limestone rubble, some of which was bonded with lime mortar, were found within the fill of the ditch. These probably represented fragments of facing stone and where part of the wall structure was toppled into the ditch during demolition.

The level at which the wall and buttresses had survived, c3.2mOD, was thought to represent the level to which the fortifications had been demolished in the mid-1800s. This was slightly lower than the level of an earlier soil horizon and the fill of the foundation trench of the curtain wall.

The area had been levelled following demolition. A layer c100mm - 200mm thick above the wall and buttresses and c300mm - 400mm thick over the fills of the ditch overlaid the site.

Cottrell, P R, 2008, Archaeological Watching Brief at Building 1, North Campus, University of Portsmouth (Unpublished document). SPM586.