The English fortress is placed within the south-west quarter of the Roman station, and its outline, roughly four-sided, was no doubt governed by the lines of the two adjacent Roman walls. It stands on the crest of the steep slope, covered, as in Roman days, by the city, and descending about 200 feet to the river. It is contained within a massive earth-bank, from 50 yards to 80 yards broad, and from 20 feet to 30 feet in height, internally of easy slope, externally steep, and which, though in substance within the Roman area, extends its skirts beyond the line of the wall, so that the Roman west gate was found buried within its substance, and a fragment of the south wall is still seen to rise through its slope. This bank measures, upon its north face, 180 yards, upon its south face 170 yards, its east 134 yards, and its west 163 yards. Here, as at York, it is evident not only that these earthworks are of post-Roman date, but that the Roman walls were completely ruined before the earthworks were thrown up. The enclosure may contain from 6 acres to 7 acres. At the south-east angle the bank swells into, and ends in, a large conical mound, about 40 feet high, and 50 feet diameter at the top. Besides this, there is a second and larger mound, about 40 feet high, and 100 feet diameter at the top, which was the citadel or keep of the place, and the site of the hall of its English lord. This mound, though near the centre of the south front, was not a continuous part of the regular earth-bank, which it here replaced. It had its own proper circular ditch, communicating on the outside with, and forming a part of, the regular ditch of the place, as is yet evident, notwithstanding much filling up.