The general use of circular and polygonal forms is first found in connection with the principal tower of the castle, the keep. The main object was at first, no doubt, the greater cohesion imparted to the masonry: the scientific advantages, from the point of view of artillery, probably were not realised till later. In France the cylindrical donjon appeared at an earlier date than in England: that at Château-sur-Epte (Eure) is said to have been begun in 1097.[195] The tower of Houdan (Seine-et-Oise) is a cylinder flanked by four cylindrical turrets: it was built during the reign of Louis VI. (1108-37),[196] and the form shows that the builders looked, not merely to the strength of the masonry, but to the reduction of the enemy’s chances of successful attack. The majority, however, of such donjons in France belong to the second half of the twelfth century and the beginning of the thirteenth, and were contemporary with our rectangular towers. But the engineers of Henry II., to whom we owe so many of our stone keeps, were certainly acquainted with the possible benefits of forms other than square. The keep of Orford in Suffolk was probably built between 1166 and 1172,[197] and is therefore earlier in date than many rectangular keeps.
Conisbrough; Keep
Internally, it is cylindrical; externally, a polygon of twenty-one sides, with three very large rectangular turrets projecting from it. It has a basement and two main floors, and is entered by a two-storied fore-building, which forms a southward continuation of the eastern turret. The sloping base of the tower is continued round the turrets, and greatly strengthens their angles; while the turrets themselves are so placed as to flank the whole tower and fore-building very effectively, and to provide additional room in the interior. This combination of the rectangular and polygonal forms is, for its date, an unique departure from the ordinary type of English tower-keep. But it must be remembered that the shell-keep on the mount usually took the form of a cylindrical or polygonal wall strengthened by buttresses; and at Orford, where the tower appears to stand upon the base of a levelled mount, we may have a conscious adaptation of this form to the heavier and loftier tower. At Gisors (Eure) the older donjon was an octagonal tower, built on a mount, and surrounded by a circular wall. The tower was probably built by Henry II. between 1161 and 1184,[198] within the somewhat earlier shell, and took the form which was best suited to the artificial soil on which it stood. But there are at least two instances of English rectangular keeps in which a slight departure from the normal form was made for obvious purposes of additional strength, without reference to an artificial site. At Newcastle the north-west turret is octagonal, with very obtuse angles. In the small tower of Mitford, on the Wansbeck above Morpeth, the north wall is built with an obtuse salient angle, so that the tower forms an irregular pentagon. The date of this tower cannot be fixed with certainty, but it probably belongs to the second half, at any rate, of the twelfth century; and it can hardly be doubted that the object of this peculiar device was to give the defenders better command of the angles of the tower which were exposed to attack from the inner ward.
Conisbrough; Keep. Plans
Somewhat later than these is the noble cylindrical keep of Conisbrough ([166]), which is attributed to Hamelin Plantagenet, a natural brother of Henry II., and husband of Isabel, heiress of William, earl of Surrey. Hamelin died in 1201: the tower was built, as the architectural details show, during the last quarter of the twelfth century. It is a regular cylinder; and to its circumference are applied six bold buttresses, which narrow slightly outwards, and rise above the parapet in turrets. The whole is built of dressed stone in large rectangular blocks, the fine condition of which, after more than seven hundred years, is extraordinary. The construction is unusually solid: the thickness of the wall in the basement exceeds 20 feet. On the first floor it is just under 15 feet: in the two upper floors it is reduced by internal off-sets, until, at the rampart level, 75 to 80 feet above the ground, it is 12½ feet. In addition to this the buttresses, which project 9 feet at the basement level and 8 feet above, are not used, like the turrets at Orford, to contain additional rooms, but are built solid. The chapel, however, was formed by constructing a chamber in the eastern buttress upon the third floor.
Conisbrough; Fireplace