The earthworks of the castle are, however, considerable. The naturally high ground was scarped and pared and somewhat raised, and near the centre of the area the highest point was surrounded by a circular ditch, the contents of which, thrown inward, converted the raised platform into an artificial mound. This, beyond doubt, was the Saxon fortress.
The rectangular area was also well defended. It had the sea for its ditch nearly at the foot of the wall along the west and south fronts. Along the east a broad and deep ditch, wholly artificial, and in part, at least, admitting the sea, ran along the foot of the wall, and divided the town from a strip of lower land, which slopes towards the Itchen, and is now covered by an important suburb. Along the north front a ditch, also artificial, was cut across the ridge; it is said, to a depth allowing it to be filled from the sea. As this would involve a depth of about 40 feet, with a corresponding breadth, the tradition is probably an exaggeration.
The north and east walls, least affected by any irregularities of ground, and nearly straight, are in length about 318 and 790 yards. The south and west fronts are curved and broken to suit the ground, and measure about 320 and 650 yards. The south-west angle is largely rounded off. Of recorded gates, there were the north or Bargate, still standing; the east gate, removed; the spur gate, remaining; the south, or water gate, removed; the west gate and the postern, preserved; Biddles, or Bridle Gate, gone; and the castle water gate, closed up.
The mural towers were chiefly drum, or half round. The north front is flanked by two drum towers, and west of the Bar is one, and east of it two, half-round. Upon the east wall, north of the east gate, was one; and, south of it, six, of which one remains, half-round, and one rectangular. At the south-east angle, the south wall was prolonged eastwards as a spur-tower, covering the ditch; this remains. Upon the south wall there were six towers, including the south flank of the spur gatehouse, and, on the opposite flank, the Bugle Tower. All but one are half-round. The west wall had many buttresses, and few towers. There was one where the south wall of the castle joined the town wall; and near the north end is a fine half round tower,—an addition.
Passing to the details, the north gate, called the Bar, is a large, handsome structure, about 60 feet broad by 60 feet deep in the centre. It is of two stages, pierced below by a central and two lateral passages, and contains above a chamber, 52 feet long by 21 feet broad, used for public purposes. In each wing is a staircase. That to the east is old, that on the west may have been so. The side passages are modern. They communicate with the central roadway by two cross arches on each side, of which the two next the north are original, and probably led into the flanking towers. An examination of the central passage shows the original gate to have been late Norman; at least a round-headed portal there placed is probably in that style, though it has rather a Decorated aspect. Then in the early Decorated time two bold half-round flanking towers were added, and still remain. At this time the rear was probably refaced, and four windows and a centre niche inserted, and the council-chamber enlarged, and probably the east staircase added. The Norman gatehouse had an upper room, of which a round-headed door, with a foliated head, remains. Next, in the Perpendicular period, a bold projection, three sides of an octagon, was added to the front. The gateway, thus advanced, is flanked by two bold, narrow buttresses, which run up to a very bold corbel table, having six machicolations in the central face, and three in each of the oblique lateral ones. The battlements are good Perpendicular, and carried round the rear towards the town; one embrasure is occupied by an alarm-bell. This gate has been much injured by restorations. The openings to the rear, archways and windows, have been refaced; but they preserve much of their old type, and have a Decorated aspect. The main passage has been cut away and widened, and the portcullis grooves are gone. When the ditch in front was filled up, a century ago, all trace of the drawbridge was lost. It appears that this bar was formerly a prison, and the curious cross arches were part of the arrangement for that purpose.
West of the Bar much of the wall remains, but is so blocked in by houses as to be invisible. Forty-six yards from the gate is the site of a half-round tower, beyond which the wall extends in a straight line to Arundel Tower, so called from Sir John Arundel, an early governor. This is a drum, 22 feet in diameter, which caps the north-east angle of the town. This tower is 50 feet to 60 feet high, and seems to rise out of a rectangular mass of masonry, possibly added to strengthen it. Here the internal level is 30 feet, or more, above the external, being a part, no doubt, of the old earthworks.
Continuing along the west wall, at 763 yards is a bold, half-round tower, 20 feet diameter, and 30 feet high, of excellent rough ashlar, with bold machicolations at the level of the adjacent curtain. This is Catchcold Tower. Built against the bank it looks solid, or like a bastion, but it is said to be hollow, though how entered does not appear. This tower, with the adjacent wall for some feet, is apparently a Perpendicular addition to what seems to be a Decorated wall. Beyond the tower is a flight of steps, modern, ascending 30 feet to the summit of the wall, which is there common to both town and castle. The wall then runs forward obliquely, probably to allow of the inclusion of the earthworks of the castle. It seems in substance Norman. The salient is capped by a rectangular buttress, the hollow angles of which on each side are crossed by low, pointed arches, pierced as garderobes, as at Porchester. This buttress tower is of Decorated date.
Then follows about 134 yards of straight wall, probably Norman, about 38 feet high, and backed to the summit with earth. Upon it a small rectangular buttress marks the junction of the north wall of the castle with the town-wall. Further on are five rectangular buttresses of various dimensions. The three first are evidently additions upon the Norman wall, the rest seem original. Part of the wall here is divided into two stages by a bold horizontal bead. Below are two narrow windows of about 18 inches opening, resembling large loops, and which seem to have had square heads. Above are traces of two windows, apparently round-topped. There must have been an interior chamber, now closed. The central buttress is broad and flat, and here are traces of the old water-gate of the castle, which must have been reached by steps, the ground behind being above 30 feet high. Close north of this water-gate is a large vaulted chamber, built against the town wall, and now closed. This part of the wall now ends in a rectangular projection, probably the root of a tower, and marked the junction of the castle south wall with the town wall.
From hence the wall is low and thin for about 33 yards, marking the end of the castle ditch, and out of the regular line, having, no doubt, been rebuilt in modern times. On the rising ground of the castle counterscarp is the root of another square tower, marking the recommencement of the regular town wall, which then turns inwards so as to protect Biddles or Bridle Gate.
This gate, now removed, opened into a steep and rather narrow ascent called Simnell-street, out of which, on the north side, opens Castle-lane, thought to represent an old entrance to the castle.