The great gateway opened in the north-west face of the curtain, and from the fragment of a jamb that remains with a bold rebate seems to have been about 8 feet high and broad in proportion. A projection inwards from the curtain shows that there was some kind of small gatehouse.
This gateway opened into a spur work formed by two curtains, 32 feet apart, projecting from the main curtain down the scarp of the ditch so as to form a parallelogram 40 feet wide by 68 feet long. The curtains were 4 feet thick and about 24 feet high. The western is destroyed, but the eastern is tolerably perfect, and at its junction with the main curtain is a shouldered postern door, 2 feet 9 inches broad, which opened on the scarp of the ditch.
At the further and lower end of the spur-work the walls turn inward (E in the plan), and again proceed parallel for 14 feet at 27 feet apart, and there contain the gates and pit of the drawbridge, beyond which a second narrowing reduces the distance to 21 feet, at which they proceed for 14 feet more, when the walls abut upon the counterscarp of the ditch, at that point revetted with ashlar. Thus the whole length of the spur-work, from the main curtain to the counterscarp, is 96 feet, and its breadths, over all, 40 feet, 25 feet, and 21 feet.
About 34 feet in advance of the great gateway was a cross wall, probably containing a second gate, and beyond it is a flight of fifteen steps, 6 feet broad, leading down into a rectangular chamber, which has had a flat timber roof, and in the opposite wall of which is a shouldered doorway, with no rebate for a door, 2 feet 9 inches broad, and 7 feet high. This opens into a low, narrow, flat-topped passage, 3 feet broad and 10 feet long, but expanded at the centre to 3 feet 6 inches, so that two persons could pass by squeezing; and at this point, in the roof, is a hole 8 inches square, evidently for the purpose of attacking them if necessary. The passage ends in a second small doorway, barred from the inside, which opens upon a bridge-pit, about 27 feet long right and left, 12 feet deep, and 10 feet broad, to a similar doorway opposite. The pit is lined with rubble below the door cills and with ashlar above, and at its west end is a hole, probably for cleaning it out, and communicating with the main ditch, of which the pit is an isolated part.
Crossing over a narrow plank bridge, the further door leads through a short, narrow passage into a chamber 13 feet square, entirely of ashlar, and having, right and left, a small door, 2 feet 9 inches broad, opening upon the counterscarp of the ditch. The doorway from the bridge had no door but those of the lateral sally-ports opened inwards. In the further, or north, wall is another doorway, also shouldered, 3 feet broad and 8 feet high, the door of which also opened inwards and disclosed a very steep flight of eleven steps, rising about 8 feet in a dovetail-shaped chamber, commencing at a breadth of 3 feet and expanding to 8 feet. It is 14 feet long. The steps land on a floor, but the walls, of which the lower 6 feet 6 inches, of ashlar, are quite perfect, have so far no openings. This singular chamber is niched into the counterscarp of the ditch, and is actually within the barbican.
The remains of the Barbican (F) are a considerable knoll of earth, having a ditch of its own, and on its rugged surface showing traces of old buildings. This covers the head of the bridge, and appears to have been approached by a winding road and entered on the west side.
This work has been the subject of much speculation. That it was the main entrance is sufficiently certain. This could only have been at one end of the main ward, and the remaining jamb is too large for a postern, and the ground at the opposite end far too steep for an approach.
The spur-work, with its lateral curtains, completely enclosed the entrance. The steps to the bridge are modern, but must represent others somewhat similar. The doors and passage were calculated for single files only, with a special arrangement for commanding the only point at which two armed men could pass. In the chamber beyond the bridge 80 or 100 men could assemble previous to a sally by the lateral doorways.
On their return, if pursued, and the enemy should enter with them, the narrow passages would make almost impossible a surprise or any sudden rush into either the body of the place or the barbican.
Further, looking to the lateral space between the walls and the great length of the bridge-pit, it is pretty clear that above the foot passage was a roadway for wheel carriages, with at least one drawbridge. Most of the passages below seem to have been flagged with stone. One drawbridge was clearly over the remaining pit; another may have covered the chamber at this time occupied by the modern flight of stairs. The thickness (4 feet) and solidity of the existing walls show that they must have been much higher, so that they would have formed lateral parapets, concealing the passage of the bridge. For this, about 15 feet might be added to the existing wall.