man plan, but the work is decided Early English. The fine circular keep of Coney, near Caen, 200 feet high, and vaulted in every story, the chateau of Gisors, and other circular towers, are executed in this style.
In the works of this period there was a tendency to economize men and material by a more skilfid disposition of the parts of the fortification.
The Norman castle held a small garrison, who trusted to the passive resistance of their walls; their successors diminished the solidity to increase the extent of their front, and by throwing out salient points were enabled to combine their forces upon any one point. A wall cannot be advantageously defended unless so constructed that the exterior base of one part can be seen from the interior summit of another; hence the advantage of buttress or flanking towers, which not only add to the passive strength of the line, but enable the garrison to defend the intermediate or curtain wall. By this means, the curtain, that part of the line of defence least able to resist the ram, became that in defence of which most weapons could be brought to bear, whilst the towers which had not the advantage of being thus flanked, were, from their form and solidity, in but little danger of being breached. If we suppose a square or polygon to be fortified by a wall, with towers at its angles, it is evident that the centre of each curtain wall, midway between its towers, will be passively the weakest part of the wall, but that in defence of which most weapons can be directed; and the centre of each tower, midway between its curtains, will be the strongest part of the work, but that in defence of which fewest weapons can be directed; or, in other words, if from the centre of a polygon we draw straight lines, passing one through each of its angles, and one midway through each of its sides, the prolongations of the former will be the safest, the prolongations of the latter the most exposed directions in which an enemy can approach.
Lines drawn from the centre of a place through its angles are called "capitals;" they are the lines of approach at present employed.
The changes introduced with the thirteenth century assumed a determinate form under Edward I., and produced the second great type of English castle, the "Edwardian" or Concentric.
