Speaking under correction, as a prolonged study of the keeps in Normandy was impossible to the writer, we should say that there is no very striking difference to be observed between the keeps of Henry I. and those built by his father. The development of the forebuilding seems to be the most important change, if indeed we are justified in assuming that the 11th-century keeps never had it; its remains can be seen at Arques, Falaise,[1152] Domfront, and Rochester. At Arques and Falaise the doorway is on the second floor, which is an innovation, a new attempt to solve the difficulty of defending the entrance. The first floor at Arques could only be entered by a trap from the second floor; at Falaise there is a stone stair from one to the other. Rochester is entered from the first floor. The basement storeys of Arques, Falaise, and Domfront are quite unlit; at the Tower the basement has had a number of loopholes, and the angular heads of those which remain suggest that they are at least copied from original lights. The main floors in Henry I.'s keeps are always of wood, but this was not because vaulting was then unknown, because the crypt, sub-crypt, and chapel of the Tower are vaulted, not to speak of many early churches.[1153] The four keeps mentioned have all three storeys, thus not exceeding Colchester in height;[1154] the Tower has now four storeys, but a good authority has remarked that the fourth storey has not improbably been made by dividing the third. No marked advance is observable in the masonry of these keeps. Arques is built of _petit appareil_; Falaise of small stones in herring-bone work; Domfront of very small stones rudely coursed; Rochester of Kentish rag mixed with flint rubble. Both Falaise and Domfront have plinths of superior masonry, but there is always the possibility that these plinths are later additions. The voussoirs of the arches at Falaise, Domfront, and Rochester are larger than the rag or tile voussoirs which are used at Colchester, the Tower, and Langeais. At Rochester and Arques provision is made for carrying the water-supply from the well in the basement to the upper floors, a provision of which there is no trace in the older keeps.[1155]