Monument MPM1093 - North Campus, University of Portsmouth

Remains of the 18th century Portsea Line of defences, chiefly consisting of a section of moat and limestone rubble walls, revealed during an archaeological evaluation in 2006.

An archaeological evaluation revealed remains of the 18th century Portsea Line of defences. The excavated area encompased a section of the ramparts made up of walls and earthworks.

The moat was probably represented by a large cut feature present at the eastern end of the trench, at least 2m deep which continued below the water table. It's edge was revetted to the north-west by a crude unstable wall made of limestone rubble bonded with lime mortar. This had been constructed at an angle of approximately 45 degrees from horizontal, and was probably a stone facing on the defenders side of the moat. Two late 18th/19th century clay-pipe stems and a fragment of brick were recovered. The fills of the moat contained small fragments of brick, and mortar and large pieces of Purbeck limestone rubble with lime mortar, which had probably come from the revertment or adjacent walls.

A wall (16) constructed from limestone rubble bonded with lime mortar on a north-east to south-west alignment, lay about 1.5m to the north-west of the moat edge. This had been truncated by a 19th century brick structure (14). The wall was at least 1.2m long, 1.5m wide and 0.2m high, and the surviving top of the wall was 0.8m below ground level at 3.3m OD. Evidence suggests this formed the outer face of an earthen parapet. A length of wall (17) of similar construction was revealed to the west of wall 16. This was at least 1.9m long, 0.9m wide and 0.5m high, and was orientated north-west to south-east at 90 degress to wall 16. The surviving top of the wall was 0.55m below ground level at 3.5m OD. This may have formed a buttress to wall 16, but the junction had been removed by the brick structure (14).

The brick structure (14), built to create a square internally-faced chamber 1.7 across, had been constructed at the junction of walls 16 and 17. This had been filled with brick rubble, which probably originated from the upper courses of the structure. The construction of the bricks, crude with small frogs, suggests a 19th century date. The purpose of the structure is unknown, although due to its position it is possible that it served some kind of defensive purpose, possibly as a magazine buried in the rampart, although this would have been very close to the face. An alternative suggestion is that it was an inspection chamber for a drainage system.

The use of lime-mortar bonded limestone rubble suggests the walls belonged to the section of defences built in 1770 , as later repairs to the defences elsewhere in Portsmouth appear to have used brick, granite and ashlar limestone.

In the north-western 4m of the trench, natural gravel layers were revealed cut by a large feature (18) which butted the stone walls. This feature (18) was possibly a gravel pit. It's upper fill contained fragments of clinker and flowerpot sherds.

Accession number 2006/1162

Garner, M F, 2006, Archaeological evaluation excavation on the site of the proposed Building 1, North Campus, University of Portsmouth, Portsmouth (Unpublished document). SPM108.