Trinity Bastion, officially known as No.1 Bastion was one of four bastions and two demi-bastions built as part of the defensive ramparts that surrounded Gosport town, known as the Gosport Lines. It was constructed, by convict labour, in about 1802 as part of the modifications to the original Bernard de Gomme defences . It protected the southern section of the moat and Haslar gate which gave access along the road to Haslar bridge.
The bastion projects southwards towards Haslar and half of the width of top of the rampart is occupied by its parapet.
Bastion No.1 mounted 14 guns in brick lined emplacements firing over the parapet. The ones at the salient angles are larger than the intermediate ones, giving a wider arc of fire. Most of them have a pivot of iron and a semicircular brick retaining wall. The original armament consisted of 24pr and 18pr smooth bore guns mounted on traversing platforms and standing carriages. In 1860 the armament list shows that the whole of the Gosport Lines held 21 x 24pr 50cwt and 20 x 24pr 20cwt with 17 x 8-inch howitzers, a total 58 guns. Expense magazines were built into the earth of the rampart behind the terreplein, four for shells and two larger ones for cartridges. These recesses survive but much overgrown. Two gun ramps from the lower levels leads up to the terreplein of the bastion on which the guns were mounted. This allowed the guns and platforms to be hauled up to the terreplein for mounting in their emplacements. The rearward wall of the bastion is a sloping brick retaining wall at its north western end. An entrance gate survives with pillars of brick.
At the foot of the rampart was a berm acting as a sentry path. The moat was retained by a brick wall. A caponier with rifle loopholes to protect the sluice which connected the moat to Portsmouth Harbour was added as part of the Palmerston modifications. One of its flanking galleries, the west one, has survived. Behind this caponier a section of the rampart and wall was later used as a school of musketry, presumably the soldiers stood on its firing step and fired across the moat. This section survives within a private yard, part of a local housing unit.
Trinity Bastion is known by local Gosport residents as ‘Vicars Bank’, due to the proximity of the Vicarage for Holy Trinity church which closes off most of the rear of the bastion. The vicarage was built by the Rev. Richard Bingham but shortly after he moved in it was required by the Board of Ordnance to be used as the residence of the Commanding Officer, Royal Engineers. (C.R.E.). Bingham fought against this but eventually acquiesced and leased the building to them for an annual rent of £100. On his death the Church claimed the vicarage and No.1 Bastion became part of its private gardens once more.
Bastion No1 is a Scheduled Ancient Monument.
The moat of Bastion No 1. is designated as a SINC Site of Importance for Nature Conservation
There is a good population of the rare Haminoea navicula: Gammarus insensibilis and Corophium insidiosum are also common. The site has therefore become one of high conservation value.
Holy Trinity: Church, Parish and People. Gosport Records No.16.
The Earlier Fortifications of Gosport by G.H.Williams.