After the Roman legions left York and Britain in about AD 400 we are not sure what exactly happened to the walls. It’s likely, however, that they continued to be crucial in attracting settlers to this spot. Even when all the buildings inside the walls had decayed, fallen or been demolished, the Roman walls still formed an impressive, defensible shield. A grant of land made during the 7th century refers to the ‘city wall towards the south and a great gate towards the west'; this wall and gateway must have been the original Roman work. The Old English name of Aldwark (meaning ‘the old fortification’), now given to a street parallel to the north-east fortress defences, implies that the Roman wall was still visible at this point many centuries after the Romans had departed.
Very little is known about what happened to the defences in the Anglo-Saxon period. The early Anglo-Saxons were not accustomed to build in stone, and did not have the expertise to repair the natural decay of the stone and mortar. There is some archaeological evidence that suggests that the fortress defences were maintained and strengthened by successive additions to the earthen rampart, which eventually, in some places, covered over the remains of the Roman stone wall.The lines of four principal roads of the fortress – including High Petergate, Low Petergate, Stonegate and Chapter House Street – survive to the present day. This suggests that the four main Roman gateways also existed and that the Roman walls continued to block other routes.
Literary evidence from the period is scarce and unreliable. Alcuin of York, who wrote in the 8th century, starts his poem ‘On the Bishops, Kings and Saints of York’ with the lines: ‘York, with its high walls, and lofty towers, was first built by Roman hands; but when he talks of the ‘lofty walls of the city’, it isn’t clear whether this refers to new, Anglo-Saxon earth ramparts or to the remains of the Roman walls. A century later Asser, a Welsh monk living in southern England wrote a ‘Life of King Alfred’, in which he says that ‘the city did not possess strong and well-built walls’ when describing York’s capture by the Vikings; but did he know that for a fact, or did he just make it up?
There would certainly have been little or no reason for the Anglo-Saxon inhabitants of York to demolish the walls, but little is known of how they were maintained. The best, but limited, archaeological evidence comes from excavation on the line the former Roman fortress defences south-west of the Anglian Tower. This has produced evidence of several phases of repair which apparently date to the 7th-9th centuries, before the Viking attack on York in 866. These repairs heightened the earth ramparts, which were capped with a timber stockade. Eventually, in some places the enlarged ramparts covered over the remains of the Roman wall.
On 1st November 866 Viking invaders captured York. Both the near-contemporary Anglo-Saxon Chronicle and Symeon of Durham, who wrote in the early 12th century, say that the city’s defences were still standing but clearly not unbreachable; but this statement of the obvious tells us nothing about the nature of the defences at that time. Under Viking rule, which lasted intermittently until AD 954, it seems that the earth rampart around at least the north-west and north-east sides of the old fortress defensive circuit was intermittently heightened.During the next two centuries, up to the Norman conquest, as the Viking-Age town flourished in the area beyond the south-east side of the defences, and the ground level there rose quite markedly, more work would have been needed to maintain a viable defence. It is, however, possible that it was at some time during the 10th or early 11th century that the south-west and south-east sides of the fortress were abandoned for military purposes and the remaining two sides were extended towards the banks of the River Ouse on the west and the Foss on the east with new ramparts, timber palisades and external ditches. This is speculation, however, and the extension may have taken place later, in the 12th or 13th centuries.
It has also been suggested that the south-west gate of the fortress survived within the Viking’s defences and formed part of a royal palace for the Viking kings. This area is now called King’s Square. This palace might have been used by the legendary Erik Bloodaxe, King of York in 948. However, what exactly happened to the defences between this time and the arrival of William I in York in 1068 is awaiting further archaeological investigation.