North of Salisbury the ground rises rapidly from the west bank of the Bourne, and the high land thrusts out a narrow neck ending in a spur towards the Avon. On the north, west and south the spur falls away in steep banks: at the centre it rises, with artificial additions, to a height of 400 ft.

In a circle round the crest of the hill is the ditch of the Norman castle, enclosing an area of a little over an acre. In a wider circle, and fitting neatly within the 300 ft. contour line, is another ditch, which once enclosed the outer bailey of the castle and the cathedral church built by St. Osmund and Roger, Bishops of Salisbury.