Monument MPM1096 - Frewen Library Extension

Several features interpreted as the outer moat and outer defensive line to the 17th century Portsmouth line of fortifications revealed during a watching brief in 2005.

The remains of what was probably the outer moat to the Town Mount Bastion and outer defence line to the 17th century Portsmouth line of fortifications were revealed during a watching brief at the site in 2005. The defences were modified during the 18th century and demolished during the 1860s.

A large linear feature (17) tapered in plan, measuring 21.7m long on an approximately WSW - ESE alignment, was interpreted as the outer moat of the later-17th century defences. This had two fills, one of which formed a steeply sloped deposit on the south side of the feature, and contained marine mollusc shells, mostly cockles, and a mid-18th century clay tobacco pipe bowl. Its position and alignment is compatible with that of the outer moat of the Town Bastion designed after 1665 by De Gomme, as calculated in relation to modern Ordnance Survey maps. The moat would have been infilled in the mid-late 18th century, and the glacis of the later redesigned defences built on top. Another linear feature (18) cut feature 17 near the centre of the same trench. This was aligned N-S, and measured over 4.6m wide at the top and was at least 1.3m deep, sloping on the west side. A further feature (24) slightly to the north, may have been a continuation of 18, although it was much narrower. This was at least 0.95m deep, and had steeply sloped sides.

To the east of feature 17, a right-angled feature (8) on a SSE-NNW alignment with roughly vertical/undercut sides was observed. This may have been a robbed foundation related to the late-17th century outer defence line beyond the outer moat, which was made up of a covered way, firing step and parapet. This had steeply sloped sides which were flared at the top. Another feature (4) which ran parallel to the north-west of feature 4 in the same trench, may also have been related to the defence line. Another feature (22) running in line with feature 4, was possibly a terminal to the latter.

A curvilinear feature (27) was observed below later deposits at the base of a trench towards the north-western corner of the site. Its fill contained a sherd of medieval pottery. A similar feature which was possibly related was observed in photographs of a trench to the west of feature 27. It is possible these features represented a natural depression containing medieval/post medieval fill related to the construction of the 17th century defences, or they could be the fill of a large feature, possibly a continuation of feature 17.

Late-19th century/early-modern features included a possible pit, tree holes and a drain trench.

Cottrell, P R, 2005, Archaeological watching brief on the extension to the Frewen Library, University of Portsmouth, Hants (Unpublished document). SPM114.