Pre-bank activity: no positive or negative evidence relating to activity before the construction of the bank was obtained in the 1975 excavations, apart from the presence of spade marks in the remaining subsoil where turves had been stripped for inclusion in the bank.
This period is marked by the construction of the following elements of the defensive system of the fortress:
A bank of dump construction made for the most part of clay, with the front and rear revetments built of stacked turf without a fronting wooden palisade. The turf would have been stripped from the area of the bank, berms and ditches; and the clay derived from the excavation of the ditches;
Three ditches, separated from the bank and each other by berms, the outer one rather wider than the inner two. These were recut on a number of occasions, but must originally have been around 1-1.3m in depth. The inner and central ditches would have been about 2m in width, the outer one 10.5m in width;
A walkway or street (intra-mural walkway or wall street) about 1.2m in width laid out around the inner edge of the bank, made of flat stones set directly on the original turf. This was probably the first feature in the defensive system to have been constructed;
A simple wooden turret at the internal corner of the bank, possibly allied with a palisade built along the top of the bank.
This period is represented by a general strengthening of the defences, which involved:
the replacement of the front turf revetment by a substantial partially mortared stone wall, originally about 1.2m wide at its lowest level. Its lowest course at the front, which formed a plinth, was built into a shallow trench, probably to stabilise its weight. Construction deposits were spread over the berm between the wall and the inner ditch, though these might also in part represent the upcast from the cleaning out of the ditches;
the cleaning out of the two inner ditches;
the probable heightening of the bank;
the construction of a small stone wall part way up the tail of the bank (inferred from its destruction deposits at the rear of the bank), possibly to revet a wall walk or platform at the top of the bank.
(Since this must have occurred before the front turf revetment had had time to collapse, this can best be placed in the early 10th century - 904-911).
A long period represented by the abandonment and decay of the defences of period 4B, with further erosion of the bank partly caused by cultivation, and the use of the W bank as a ridge in a ridge and furrow system.