Monument MPM1432 - Remains of the West Bastion, Hilsea Lines

The remains of the West Bastion of the 1858 Hilsea Lines revealed during an archaeological evaluation in 2013. Features included a series of foundations belonging to the eastern section of the main gate, an armaments store, and the north and south gun batteries. This section of Hilsea Lines was demolished in the early-1930s.

The remains of the West Bastion of the 1858 Hilsea Lines were revealed during an archaeological evaluation at the former Hilsea Bus Depot site in 2013. A series of foundations belonging to the eastern section of the main gate, an armaments store, and the north and south gun batteries were recorded, together with layers relating to the demolition of the Lines for the Hilsea Bus Depot in the early 1930s. Features connected to drainage, and a pathway running behind the defences were also observed.


Foundations Overview

The foundations ran northeast-southwest across the former Hilsea bus depot site, the section exposed measuring 73.5m long and 17m wide. They formed the west side of the West Bastion, comprising the east-west gate structure, a block of rooms (probably an armaments store), and the north and south gun batteries. The section exposed showed a uniform foundation plan which supported a series of casements and vaulted chambers housing the guns and their crews. In the north and south batteries thick internal walls were positioned at right angles to the exterior walls, dividing the space into cells. Above ground the cell walls were pierced in order to join five gun chambers together in each gallery. Thinner opposing curved foundations within these cells supported wheels for traversing platforms for guns on the outside of the defences, and on the inside formed the foundations for iron blast shields protecting the living quarters of the gun crews. The arrangement of the walls was different in the south west corner of the site, where there were a number of rectangular rooms with very thick brick walls, and supporting walls for wooden floors. This section may have been used as an armament store.

The lower part of the foundations consisted of poured concrete, varying between 500mm - 1.7mm thick, off of which brick walls had been built. Both the external walls and internal linking wall contained relieving arches which were eight courses of brickwork thick. These mirrored the arches which had supported a bomb-proof roof above ground.

East-West Gate

The main gate which provided access through Hilsea Lines was formed of two arches which controlled the traffic entering and leaving Portsea Island via the London Road. The eastern edge of the gateway lay within the Hilsea Bus Depot site.

The remains of the east-west gate structure consisted of a number of walls which ran north-south or east-west. These had been much disturbed by the construction of the bus depot. The remains of the external wall measured 0.67m wide and 1.9m deep. It ran 5.17m southwest-northeast from the armaments store, and then turned west where it formed the rear face of the entrance. A number of construction trenches and wall foundations belonging to the gate structure were revealed during the evaluation, including what may have been the flanking wall for the pedestrian arch.

Armaments Store

The armaments store formed the southernmost part of the west face of the West Bastion and joined the gun batteries to the gate. It occupied a cell 11m wide. The store had been divided into two halves, one to the north and one to the south. The northern half was divided into two rooms, the southern half into three. A series of construction trenches and foundations belonging to the store were revealed. These included the foundations to the front, rear and exterior walls. The front wall had an inner and outer wall, giving it a double thickness. This wall continued to form the face of the south battery to the northeast. The rear wall of the store, which measured 2.1m wide and 2.1m deep, was the thickest wall encountered throughout the site. There was no evidence of an opening in this wall. The face of the exterior wall was formed from inverted arches bonded to pillars of English bond, each of which marked the position of a gun. Courses of tiles and bricks had been used to level off the arches, creating a level surface on which to build the section of the wall above ground.

South Battery

A 2.3m wide cell was positioned to the northeast of the armament store, and probably formed an entrance into the gun gallery. The South Battery itself had been divided into five cells, each of which would have housed a gun. The dividing cross walls ran in a northwest-southeast direction, linking the front and back external walls of the battery. The walls were built on concrete foundations in construction trenches measuring 11.16m long, 1.8m wide and 2.9m deep. There were also two curving walls within each of the cells. The construction trenches for the walls measured 3.19m long, 2.2m deep and 1m wide. Within two areas of the battery brick walls bonded to the internal and external walls would have divided the accommodation for the gun crews in half. A series of construction trenches and walls relating to the south battery were revealed during the evaluation.

The defences turned northwards between the north and south batteries, creating a wedge-shaped space between them. A curved brick wall 3.19m long and 1.2m deep joined the north wall of the south battery to the south wall of the north battery. A rectangular brick structure measuring 3.85m long, 2.14m wide and at least 1m deep, was bonded to the east side of this wall.

North Battery

Four out of the five gun cells were observed in the north battery, each of which had been divided by cross walls running in a northwest-southeast direction, linking the front and back external walls of the battery. The walls were constructed from brick above a concrete footing and measured 11.16m long, 1.8m wide and 2.9m deep. Curving walls within the cells measured 5.13m long, 1m wide and 2.2m deep. A partition wall bonded to the internal and external walls would have divided the accommodation for the gun crew in half. A series of construction trenches and walls relating to the south battery were revealed during the evaluation.

A different construction method had been used for the walls of the north battery, compared to that of the south. The outer wall was thinner, and the inner wall thicker, making them more equal in thickness. This may indicate changes in technique during the 13 year programme of works, or different contractors working on each of the batteries.

Pathway

A gravelled pathway measuring 3.53m wide, constructed in a trench 0.42m deep, was observed behind the Lines. The lower part of the trench had been filled with a 200m thick layer of rectangular granite setts (cobbles), laid in an irregular pattern. The cobbles measured on average 370mm long, 133m wide and 90mm deep. Above the cobbled layer was a 220mm thick layer of well-compacted granite gravel.

Drainage

A construction trench for a manhole and iron pipe was observed to the south of the Hilsea Lines. The manhole measured 1.17m long, 0.88m wide and was at least 0.3m deep. The cast iron pipe had a 109mm diameter, and ran east from the manhole for 37m. A second cast iron pipe bringing water from the Lines ran to the north.

In the south of the site were drain gullies which would have taken water from a down pipe that drained the arched structure which formed the upper part of the Lines. The construction pits for the gullies contained brick structures which measured 400mm long, 315mm wide and 120mm deep, and fragments of the cast iron down pipes.

Demolition

Two layers which probably related to the demolition of Hilsea Lines in the early 1930s were observed. The first was clay loam layer which contained abundant bricks, mortar, cobbles and concrete fragments. It was 300-700mm thick and covered the majority of the Lines. The second layer consisted of a silty clay loam containing abundant cobbles and some brick fragments, and was located towards the north east of the site. This layer was 400mm thick and may have been associated with the destruction of a roadway which was located in this part of the site.

Accession No: 2013/850

Anderson, E L, Russel, A D, 2014, Report on the Archaeological Evaluation and Watching Brief at the Hilsea Bus Depot site, Portsmouth (Unpublished document). SPM258.