As part of the major civic works building spree that occurred during late 1st century and 2nd centuries, a fortified garrison was constructed in the north-west corner of the city, centred on the modern day streets of London Wall and Wood Street.
The walled fort was completed in about AD 120 and was square in layout, each side being approximately 200m (655ft) in length with gatehouses situated in the middle of each of the four walls. Stone towers stood at each corner with several more turrets or bastions spaced along the walls. It is thought the fort provided barracks for about 1000 troops.
The walls of the fort were constructed of Kentish ragstone, the same material used later in the construction the city walls. The boundary walls are thought to have stood to a height of 4.5m (15ft) with an original width of 1.2m (4ft).
The fort began to be decommissioned after only about 100 years of usage, and it’s buildings dismantled. The troops were likely accommodated elsewhere in London especially in Southwark.
The north and west walls were retained and became incorporated in to the new city wall. These two walls of the fort were widened by the addition of a second wall constructed against it’s inside face to bring the whole to the same height, width and standard as the rest of the new city wall.
Evidence of the original western fort walls, and their subsequent widening can be seen in the remains that are exposed along Noble Street, and the remains of the fort’s West Gate are occasionally opened to the public next to the entrance of the London Wall underground car park.