Military Architecture in England During the Middle Ages

by A. Hamilton Thompson

The development of the castle during the twelfth century was governed, as has been explained, by the methods of attack which its defenders had to meet. The strong fortresses of the reign of Henry II., with their stone curtains and rectangular keeps, opposed to the enemy a solid front of passive strength which defied attack. Sufficiently provisioned, a small garrison was capable of holding out against a long blockade, and tiring the patience of the assailants, whose artillery could make but little impression upon the masonry of the castle. At the same time, the stone castle with the rectangular tower-keep does not represent a final point in the perfection of fortification. The early Plantagenet castles were, on the contrary, merely a departure from the ordinary type of castle, composed of earthwork and timber, in the direction of an organised system of permanent stone castles. They belonged to a transitional period; for, even while they were being built, improvements upon their most striking feature, the rectangular keep, were suggesting themselves. During the last twenty years of the twelfth century, lessons learned by the Crusaders from the traditional methods of fortification employed in the Eastern empire exercised a profound influence upon the military architecture of France and England; and the application of these lessons during the thirteenth century entirely altered the defensive scheme of the castle, until the plan of masterpieces of fortification like Caerphilly and Harlech presented an entire contrast to the plan of defensive strongholds like Norham and Scarborough.

The first necessity which had governed the development of fortification was that of enclosing the defended position so as to present an adequate barrier to attack. The bailey was surrounded with its palisade; while the palisaded mount, with its wooden tower, commanded—that is, overlooked—the operations of the defenders within the bailey, and provided a second line of defence, if the bailey were taken. As siege-engines increased in strength, stone-work took the place of stockading. The bailey was encircled by a stone wall with a certain number of towers on its circumference. It was sometimes divided into an outer and inner ward by a cross-wall, or, as at Ludlow ([96]), a large outer bailey was added to it, which formed a courtyard for barracks and stabling, and a protection in time of war for dwellers on the outskirts of the castle and for their flocks. A wall superseded the palisade round the mount, or a strong tower was built, either in connection with the mount or on a new site, which commanded the whole enclosure. Thus the passive strength of the castle was ensured. But stone walls and towers, however strong, were in themselves an insufficient protection, unless the defenders could keep themselves fully informed of the movements of the enemy. It was necessary that they should be able to command the field in which the besiegers worked, and especially the foot of the wall or tower on which the attack was concentrated. The battering-ram, the scaling-ladder, and the mine must be kept under constant observation. A first step towards this was the establishment of projecting towers along the wall at intervals. These flank the wall—that is, the outer face of the wall between them can be overlooked and protected by bodies of men posted upon the projection on either flank. At first, however, the system of flanking was far from perfect; and therefore the next step was in the direction of improving it, so that every portion of the outer surface of the enceinte might be covered by the fire of the defenders. This improvement, which we are about to trace, was effected gradually, (1) by a change in the form of the flanking defences themselves; (2) by their multiplication at more frequent intervals. The first of these changes begins to be noticeable during the later years of the twelfth century: the second was brought to pass in the first half of the thirteenth century, and led to further developments in the arrangement of the lines of defence.

The rectangular form of the keep and of the towers on the curtain was in two respects a drawback to the defence of the castle. In the first place, the salient angles of the masonry were liable to destruction by sap and mine. The parallel jointing of the stonework made the removal of fragments of stone by the bore or pick at these points a comparatively easy, if still laborious, task. In the second place, the angles of a tower or curtain, which were thus points of danger, were precisely the places which the defenders were least able to command satisfactorily. Each face of a rectangular tower commands the field immediately in front of it: the range of shot, from the point of view of each marksman, is in a direction at right angles to the face of the tower. Strictly speaking, the foot of the whole curtain and its towers lies within a “dead angle,” as vertical fire from the rampart is impossible; but the wooden galleries attached to the rampart obviated this difficulty. But, if the lines of two adjacent faces of the tower are produced, it will be seen that the space contained by these is out of the defenders’ range, and within it miners can work securely, while the main attack is directed against the faces of the rectangle. One obvious concrete illustration of this is seen at Rochester. When King John, in 1215, besieged the castle, he directed against it his stone-throwing engines. Finding that progress by this means was slow, he set his miners to work. A breach was made in the outer curtain, and the miners continued their operations on the tower, and eventually, after much difficulty, broke their way through it.[192] We can see to-day that the south-east angle of the tower has been rebuilt, and that the form of the reconstructed turret is round, and not square. This, no doubt, marks the place where the breach was made: the repairs are evidently part of the work taken in hand by Henry III. in 1225.

A further weak point in the defences of the castle was the insufficient flanking of the curtain. In the eleventh century, as we have seen, flanking towers were discouraged by feudal over-lords, who rightly recognised the danger which a strongly fortified castle, in the hands of rebels, might mean to themselves. As time went on, stone curtains were provided with towers; but these were not many in number, and, so long as the rectangular form of tower continued in fashion, long spaces of straight wall were left between the projections. The risk of providing too many salient angles was probably recognised by military engineers. From the flanking towers the adjacent part of the wall could be covered by the artillery of the defence; but, where a long interval existed between two towers, the wall mid-way was out of effective range. To protect these unflanked points in time of siege, a body of defenders would have to be kept on each spot. A twelfth-century castle, therefore, to be thoroughly defended, needed a large garrison to cover its numerous weak points. Any attempt to concentrate the defence upon one threatened spot might lead to the weakening of the defence at other points, of which the enemy would not be slow to take advantage.

Added to this was an inherent drawback in the normal plan of the castle. Its wards and keep provided a system of successive lines of defence, which caused an enemy immense trouble to pierce, but could not offer a combined resistance to him. In many castles, like Norham or Barnard Castle, the inner ward and keep were placed at a distant angle of the enclosure, and were protected from external attack by steep outer slopes and a river at their foot. In such cases, the wall of the outer ward offered the first resistance: the inner ward did not come into action until the enemy had entered the outer ward, and the defenders had to retire to the inner enclosure. If the inner wall was breached or stormed, the keep gave the defence its last shelter. At Château-Gaillard, as has already been described, the chief feature of the siege was the capture of ward after ward: the defenders, in despair, did not even attempt to resort, as a final resource, to the keep. Château-Gaillard was in its own day a model of scientific fortification. Its fall was therefore a very striking example of the disadvantage of successive lines of defence, of which only one could be effectively used at a time. It is true that here and there, as at Rochester, the keep was placed so near the curtain of an outer ward that the exterior of the castle could be commanded from its battlements, and its artillery could be brought into play over the heads of the defenders of the curtain. At Richmond, the great tower commands the one side of the castle from which attack was possible, and was thus placed in the very fore-front of the defence. But such arrangements were happy ideas which occurred to individual engineers, and do not imply any systematic advance in the science of defence.

Château-Gaillard; Plan

The experiences of the earliest Crusaders brought the warriors of the west face to face with methods of defence far superior to those employed in England and France. The city-wall of Antioch gave them an example of a perfect system of flanking defences; and, in the triple enceinte of Constantinople they saw how successive lines of defence could be used in co-operation. At Antioch the wall was flanked at frequent intervals by fifty towers. Each of these, rising above the curtain, commanded not only its space of intermediate wall, but the rampart-walk as well. The rampart-walk, moreover, passed through the towers, which were protected by strong doors. To gain the whole line of wall, therefore, it was necessary to occupy the towers, each of which could be converted into a separate stronghold, isolating the intermediate rampart-walk. The siege was badly conducted, the Crusaders limiting themselves to a strong position between the city and the Orontes, and allowing the defenders to hold their communications on two sides of the city open for some five months. Posts of observation were eventually established on the two neglected sides; but the actual capture of the city was due to the treachery of one of the commanders of the Turkish garrison, who admitted a body of Franks into one of the towers in his charge. They made their way into seven more towers, and so gained access to the city.[193] The three walls of Constantinople surrounded the whole city: each was higher than the one outside it, so that all three could be used simultaneously by the defenders.[194] Against such a system of concentric defence, the besiegers were manifestly at a disadvantage.

These lessons from the east, stimulating though they were, did not produce their full practical effect for some generations in the west. Our engineers had to pass through a long epoch of gradual experiment before they could arrive at a finished system of flanking or of concentric lines of defence. The traditional mount-and-bailey plan provided the foundation of the plan of the stone castle. The traditional importance of the keep as the ultimate place of refuge dictated the arrangement of ward behind ward, culminating in the great tower. Meanwhile, the improvement of flanking defences led more and more to the concentration of engineering skill upon the curtain, so that the keep gradually took a place of secondary importance. As an obvious result of further improvement, the keep was dispensed with, and the whole attention of the engineer was directed to combining the defences of the castle into a double or triple line of simultaneous resistance to attack. These steps took time: the transition from one to the other was effected by no sudden revolution, but by work along old lines, a work of revision and improvement, until the finished product formed an almost complete antithesis to the source from which it was derived.

The earliest signs of transition in England are seen in the strengthening of the masonry by the reduction and elimination of salient angles. It is obvious that, if a rounded or polygonal form is given to a projecting tower, or if the angle of a rectangular tower is rounded off, a wider field will be commanded by the artillery of the defence. The new range will be a large segment of a circle radiating from the centre of the tower, instead of a rectangle in front of each face. The sectors at the angles within which an attacking party can work securely will be thus eliminated, and the chances of the success of a mine will be less. The masonry also will offer much greater resistance to the battering or boring engines of the enemy. The joints are no longer parallel, but radiating, so that it becomes much harder work to force out stones and effect a breach. The obtuse angles of polygonal towers, with the joints of the masonry in the alternate faces running in oblique directions to each other, have a much greater power of resistance than the right angles of the ordinary twelfth-century tower.