The castle is placed in the south-west quarter of the Roman station, high above the city and the valley of the Witham, which lie to its south and east, and somewhat elevated, artificially, above the table land to its north and west. Its walled _enceinte_ lies just within the Roman area, to the adjacent limits of which its southern and western fronts are roughly parallel. The curtain wall, a very remarkable, and, on the whole, a very perfect work, is built upon the ridge or central line of the earth-bank, and therefore contains the same space, and is in circuit about 650 yards; it is from 8 feet to 10 feet thick, and 30 feet to 35 feet or even 40 feet high, exhibiting much herring-bone work, and certainly of Norman, and possibly early Norman, date. Opposite to the great mound, where the earth-banks cease, the wall is continued across the ditch and up the slope of the mound, as at Tamworth and Tonbridge. To enable it to reach the level of the battlements of the keep, it is raised by steps to the point of junction, and there contains chambers which will be more conveniently described with the keep. In the wall are two principal gates, one to the east, opening into the upper city, opposite to the Exchequer Gate of the Close, and the other to the west, opening direct into the field. Besides these there is a small door opening towards the south upon the lower city, and a door in the keep in the same direction. The main entrance is placed in the east wall at about 40 yards from its south-east angle. The west gate stands in the west wall, about 30 yards from the north-west angle, which length is thrown back at a very obtuse angle, probably to avoid the remains of the Roman west gate, which stood about four yards in front of it. Both east and west gates are of Norman date, and were originally much alike, each being a plain arch, placed in a rectangular bay or recess in the wall, 18 feet wide by 10 feet deep, instead of, as was more usual, in a regular square gatehouse, as at Tickhill, Porchester, and Sherborne. The bay may have been closed in the rear by a cross-wall with a second archway, of which there is an indication at the west gate. There was an upper chamber with a timber floor. At the east gate the arch is full centred, of 14 feet opening, without chamfer or rebate, or ornament of any kind. Probably there is a portcullis groove, but if so it is blocked up and completely concealed by the woodwork of the modern doors. It is certain that the main entrance of a Norman castle could never have been so constructed that there should be no rebate against which the door should be pressed when closed, and probably the fitting was composed of a ring of stones inserted, as in the doorway in the cross-wall of Rochester keep, without bond, into the exterior arch. Over the door is a pointed window, probably an early English or early Decorated insertion. Later in the Decorated period, this gateway has been masked