Monument MPM1548 - Former Portsea defences, HMS Nelson

Evidence of the former 18th century Portsea line of defences recorded during a watching brief at HMS Nelson in 2013. A series of deposits revealed in trenches and bore holes across the site were interpreted as relating to the moat and counterscarp wall, covered way and glacis.

Evidence of the former 18th century Portsea line of defences was recorded during a watching brief at HMS Nelson in 2013. A series of deposits revealed in trenches and bore holes across the site were interpreted as relating to the moat and counterscarp wall, covered way and glacis. The Portsea defences were made up of a series of bastions and demi-bastions, connected by curtain walls and protected by outworks consisting of two ravelins and a demi-redoubt. The development site lay immediately to the east of the site of the Duke of York's Bastion, located approximately in the centre of the defensive line.

The watching brief revealed that during the demolition of the defences in the 1860s the walls and earthworks had been levelled unevenly, to about 4.00m-4.2m AOD, 1.30m-1.45m below the modern ground level. The moat had been backfilled, probably with material taken from the levelled earthworks. As only a small amount of stone rubble was recorded on the site, it is likely that stone from the walls was reused elsewhere, possibly for the foundations of the Unicorn Buildings which were constructed on the same site shortly after demolition took place. However, it is possible that a substantial obstruction encountered in one pile hole during development work may have been the surviving foundations of the counterscarp retaining wall.

The base of the dry moat was 6m below the current ground surface. The backfill of the moat consisted of a deposit of silty clay loam which contained brick fragments and gravel inclusions. Beneath the backfill was a deposit of black organic silty clay loam, interpreted as soil which had accumulated at the base of the moat.

The wet moat was 3m deep, the lower 2m of which was filled with soft deposits, probably formed from re-deposited natural soil. This would indicate that the moat silted up quite rapidly. These deposits were overlain by approximately 1m of black organic material, from which a fragment of a leather belt strap measuring 30cm in length by 25mm wide was recovered. Although this deposit had a high concentration of organic matter, the black material did not contain any animal bone or pottery, suggesting that it was not related to the disposal of rubbish. Both deposits would suggest that the moat was not cleaned out during its 100 year lifetime. The findings revealed that the wet moat was slightly wider than had previously been thought.

Accession No: 2013/898

Russel, A, Cottrell, P, Fedorowicz, A, 2013, Archaeological Watching Brief on land at HMS Nelson, Queen Street, Portsea, Portsmouth (Unpublished document). SPM278.