Monument MPM1680 - Former Sea Line Wall, Gunwharf

The remains of sections of the former Sea Line defence wall to the 17th century town defences, revealed during an archaeological evaluation in 1997.

The remains of sections of the former Sea Line defence wall were revealed at several locations during an archaeological evaluation at the Gunwharf Quays site in 1997. The wall had been situated on the west side of the 17th century Portsmouth town defences designed by Sir Bernard De Gomme, and was probably constructed between 1668-85. It incorporated three bastions with gun emplacements (a triangular bastion in the centre and angled bastions at either end), and was designed to protect both the inner defences from vessels trying to land on the seaward side, and the road which ran from the town to the dockyard. The Sea Line wall was demolished between 1797-1808 to make way for the boundary walls and entrances to the New Gunwharf and Gunwharf Barracks. However, the archaeological evaluation suggested that some sections of the wall may not have been demolished until the 1920s.

Remains of the Sea Line wall, and part of the west wall to the northern angled bastion (located opposite Beeston's Bastion) were observered in five trenches across the Gunwharf site:

Trench 3 (approximate NGR SZ63179986, corner of former Dolphin Way and Scott Road)
The remains of the wall survived to a depth of approximately 1.6m below ground level, and were around 1.3m wide. The facing stones to the outer (west) wall had been removed to at least a depth of 3.5m. The area either side and above the wall had been backfilled during the 1920s when the sea wall was partially demolished and the Basin infilled. This section of the Sea Line wall would originally have abutted the quay wall to the New Gunwharf (built 1797-1808) to the west, but no trace of the latter was found.

Trenchs 4A & 4B (approximate NGR SZ63189988, East of Scott Road)
The top of the wall was encountered between 68-108cms below ground level. It measured approximately 180cms wide. The outer (north) face of the wall had been constructed using smooth limestone blocks (possibly Purbeck) and the facing blocks were cut at a slight angle. The inner (south) face was vertical, and had been constructed using less regular blocks. The core of the wall, between the outer and inner walls, comprised small stones set in lime-based mortar. Either side and above the wall was a loose fill of demolition debris made up of brick, stone, mortar and tile. A black layer above the fill contained pieces of coal and coal dust. This deposit dated to between the late-1870s and 1900 when Mill Redoubt was demolished and the mill pond infilled.

Trench GW243 (approximate NGR SZ63179981, north of Nelson Gate)
The wall was encountered 48cms below ground level. It measured 2.05m wide at the top, and its core (between an inner and outer face of stone blocks) consisted of smaller stones set in a lime-based mortar. The facing blocks on the outer (west) side of the wall survived within 73cms of the modern road surface, and were slightly battered/angled. The outer face was excavated to a depth of 3m below ground level, where a natural clay deposit was encountered below the fills which had been used to make up the ground for the New Gunwharf.

Trench GW244A (approximately SZ63169976)
The remains of the outer (west) side of the wall to the angled bastion situated at the northern end of the Sea Line defence wall, were revealed 1.30m below ground level. The wall was at least 1.4m wide, and the facing stones had been removed.


2013/112

The Conservation Practice, 1997, Gunwharf Quays, Portsmouth, An Archaeological Evaluation. Part 1: Desk Top Study (Unpublished document). SPM327.

The Conservation Practice, 1997, Gunwharf Quays, Portsmouth, An Archaeological Evaluation. Part Two: Site Investigation (Unpublished document). SPM326.