The roof was conical, and rested upon an internal wall, outside of which was the rampart walk, protected by an unusually lofty parapet, surmounted by a heavy bold coping, and pierced by twenty-four doorways, intended to open into the timber _brétasche_, while between the doorways are twenty-four loops, intended to be used when the _brétasche_ was not fixed. A curious evidence remains of the manner in which this tower was scaffolded. A double row of putlog holes are seen to wind round the tower spirally, in two parallel lines, showing that as the wall rose it was surrounded by a sloping roadway of timber, of which the main beams were thrust into the wall, and supported by struts, the lower ends of which rested upon blocks in the lower holes. A similar arrangement may be seen in the north-west tower of Harlech Castle, commencing at the top of the curtain-wall. So strong was Coucy keep that when, at the command of Mazarin, powder was exploded in its basement-chamber, and the vaultings throughout, thus lifted, fell, the cylinder, though cracked, was not thrown down. This noble example of a thirteenth-century tower has been successfully repaired by Viollet-le-Duc, who closed the fissure, and made the tower apparently as sound as ever. The vaulting, however, is gone. Nor does Coucy, though the chief of the towers of the thirteenth century, stand alone in its magnificence. Issoudun, known as La Blanche Tour, is remarkable for the position of its entrance-door, and for its well-stair contained in the projecting spur; Tournebut, Cosson, Verneuil, Chinon, Villeneuve-le-Roi, Semur, Alluye, Bourbon-l’Archambault, and Châteaudun, are a few only of the round towers or donjons scattered over France, and dating from the latter half of the twelfth and from the thirteenth century. There is a peculiarity in these French towers unknown in England. Where, as at Château-Gaillard, they are exposed on one side to be battered, they are constructed with a projection forming a right-angled salient from the cylinder, which thus becomes keel or boat-shaped in plain. This spur has a fine effect, and being usually solid, adds much to the strength of the tower. This projection, of which Roche-Guyon is a fine example, and which ascends the whole height of the tower, is very different from the spur-buttress, by which a round tower rises from a square base. This is especially common in Wales, and may be seen producing a good effect both at Chepstow and Goderich. Of cylindrical keeps, either of early English or late Norman date, in England, may be mentioned Brunless, near Brecon; probably Caldecot, Monmouthshire; Coningsborough, described above; Dolbadarn, in North Wales; Launceston; Pembroke; Penrice, Glamorganshire; Skenfrith, Monmouthshire; and Tretower, county Brecon. The round tower at Barnard Castle, a very fine one, already mentioned, is later.