Can these novelties have come into use before the Conquest? If so, we must presuppose a growing acquaintance with building methods as pursued in Normandy. This is not improbable. Norman influence was felt in English life during the reign of Edward the Confessor,[44] and imitations of Norman, as at an earlier date of German, technique are not beyond reasonable imagination. But it must be acknowledged that, while we are fain to discover the germ of Anglo-Norman art in these simple monuments, the constructive, purely architectural quality, which is the essence of that art as manifested at Durham or in the west front of Lincoln, is totally absent from them. That essential quality is not a home growth, but a foreign importation. The chief element of structural transition in these towers is to be found in their growing spaciousness. Areas which are on an average oblongs of some 10 feet 5 inches long by 10 feet 8 inches broad grow at Caistor to 15½ by 17½ feet, and at Harpswell to about 15 by 16 feet. With the growth of the area the wall thickens, thus affording a contrast to towers like Hough, where the large area is enclosed by thin walls. The eastern wall of the tower at Alkborough is less than 2½ feet thick; the average thickness of such walls is about 3 feet 7 inches. At Caistor the wall is 5¾ feet thick. One cannot fail to recognise that the slender tower of Saxon type, while keeping its unbuttressed character and its “mid-wall” arches, is spreading out into the ordinary broad and heavy Norman tower.