The Royal Citadel, designed by Charles II’s chief military engineer Bernard de Gomme, is one of the very few surviving examples of a permanent seventeenth-century fort in England. Though its outworks were demolished late in the last century when its military value had ceased, the main building is still intact. It was built shortly before the Frenchman Vauban brought the art of geometrical fortification to perfection, and Pepys, who inspected it, expressed the opinion that ‘de Gomme hath builded very silily’. Possibly one of the defects he had in mind was the carrying of stonework to the full height of the ramparts, instead of finishing them in cannonball-absorbing earth, with the guns pointing through stone-faced embrasures. Had it ever faced a siege, this would have risked the gunners being driven from their pieces by stone splinters. But it never was attacked, and the appearance today is all the more picturesque.
The main ramparts were laid out on an irregular plan designed to fit the ground on which they stood. Siege was possible only from the west and north, and here they show straight ‘curtains’, with projecting bastions whose flanks covered the curtain and the face of the adjoining bastion with cannon and musketry. The bastion faces could give a converging fire on any point; and two triangular ravelins, lower than the main building, covered the approaches to the bastions. A vertical-sided dry ditch protected the ramparts, and outside this was .a low regular slope or ‘glacis’, designed to bring an assault direct into the line of fire from the parapets. On the outer side of the ditch, and sheltered by the rim of the glacis, was a covered way, which served for an outer musketry line and for assembling sorties.
On the south and east the ground falls steeply, and no assault was possible. Here outer defences were therefore not needed, and the slope was regularly scarped below the batteries covering the sea approaches. Plunging fire from the upper ramparts could be aided by the horizontal gunnery of the Lower Battery, built on the rocks at the water’s edge, which also gave a protected communication with the sea in case of blockade by land.
It has often been said that the object of the Citadel, like that of a Norman town castle, was as much to overawe Plymouth as to protect it: and Charles may well have had in mind the disastrous effect of local resistance to the royal cause in the recent Civil War. Certainly it completely dominated the town, and no revolt was feasible as long as its garrison remained loyal. But in 1688 the Governor promptly declared for William of Orange, and the Stuart cause in the South-West was lost. The Citadel is still occupied by a detachment of Royal Artillery, and part of the ramparts, with guns in position, is open to the public.