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HISTORY OF ENGINEERING.
Book T.
these were crowned with a parapet, resting on corbels, and in the centre division betweenthe towers were deep and projecting machicolations, from which might be hurled a varietyof missiles upon the heads of those who had crossed the drawbridge, or were endeavouringto force the portcullis or fire the gates.
Catapult®, mangonels, balist®, springals, tribuli, arcubalista?, multones, barfreni,skaffauts, and various other instruments and machines were here lodged, ready either fordefence or attack.
On comparing these defences with those attached to the entrances of Roman or Greekcities, we find that the orders of architecture are omitted, but many oriental contrivances aresubstituted, which give a peculiar effect and character; there is the same solidity of con-struction and quality of material in both, as well as great similarity of workmanship. Allthe vaults and arches, winding stairs and passages, are formed in the same manner ; concreteis universally employed, to fill in between the outer faces of the walls in the castles of themiddle ages as in those of the Roman fortress. The construction is Roman, and themilitary features are mostly of eastern origin.
The lower or entrance floor of Saltwood Gateway has considerable strength; it isflanked by two circular towers, which contain hexagonal apartments.
From out to out this gateway measures 56 feet 6 inches, and the space between thetowers is 12 feet 2 inches. The entire depth, from the face of the wall between the towersto that at the rear, is 56 feet 6 inches.
The floor above contained many convenient apartments, admirably proportioned, and soarranged as to be used for defence when occasion required. Each of the towers had achamber, 13 feet 2 inches in diameter, lighted by two narrow windows, between which wasa fireplace, the flue being continued to the summit of the tower.
A spacious room, 29 feet by 17 feet, and another 16 feet by 15 feet, occupied the spaceover the gateway ; the walls are 5 feet in thickness, except where the towers unite with thestraight portions, and there is a square mass of masonry and rubble, solid throughout,except where hollowed out for the purposes of obtaining a guard room, 8 feet by 4 feet.
Bridges . — We have no evidence of any bridges of consequence being erected previous tothe Norman conquest , and the names of our principal towns on the banks of rivers, havingthe word ford attached to them, seems to confirm the opinion that none existed. Followingthe course of the Watling Street, or great Roman road over the Medway, we meet withAylesford; over the Darent, Dartford ; the Cray, Crayford; the Ravensbourne, Deepford ;and so with most other rivers in England. The capital in all probability would first havea bridge in preference to a ferry, which is noticed over the Thames . We have an accountof a timber bridge constructed by Etheldred in 1002, which lasted many years, and also ofanother built in 1165.
The first stone bridge was begun in 1176, by the celebrated Peter of Colechurch, whocontinued the work during the reigns of Henry II., Richard I. , until the second year ofthe reign of King John , when he died, and was buried in the crypt of the chapel erectedover the centre pier.
It appears to have been the custom with the society called the Brothers of the Bridge,when any member died during the superintendence of any important work, to have his