There now remain for discussion lantern towers of square plan. This was the form almost universally employed in Normandy, England, and churches which came under Norman influence, especially in the earlier Gothic period. During the Romanesque epoch such lanterns were wooden roofed. But with the introduction of the ribbed vault, an eight-part vault was devised for this crossing, whose severies were precisely like those above the windows in six-part vaulting, from which, in fact, this new type probably developed. Most of the towers originally wooden roofed have since been vaulted, and it is therefore difficult to judge of their original character. Their imposing interior appearance, however, may be judged from the ruins of the abbey church of Jumièges (1040-1067). It would seem, from the places for beam ends left in the wall, that such lanterns as this were generally roofed with a flat ceiling above the first stage of openings, the second series probably forming a belfry. It is natural, therefore, when vaulting comes in, to find it placed at the level of the former flat ceiling with only the lower openings used as windows, leaving the walls above to offset the thrusts of the vault by their downward pressure. A somewhat rudimentary vault of this eight-part character may be seen in Saint Georges-de-Boscherville,[328] in which the wall arches are omitted and all the ribs made to spring from corbels. This, of course, is because the Norman Romanesque crossings were not originally planned for vaulting. A little later, wall ribs were regularly used, and in Saint Yved at Braisne (consecrated 1215)[329] the four major ribs have their supports running all the way to the floor, while in the cathedral of Laon (after 1165) (Fig. 60) even the eight wall ribs which rise from the corners of the tower are similarly carried down. Of course the intermediate ribs necessarily rise from corbels, but in the developed crossings of this type such corbels are placed as near as possible to the crowns of the four great arches of the nave, choir, and transepts. Similar lanterns are to be seen in the church of Notre Dame at Cluny, and in Saint Maclou at Rouen (lantern cir. 1511),[330] where, however, ridge ribs are added in each of the eight cells. Notwithstanding the examples cited, the use of a lantern is not common in developed Gothic architecture. This is perhaps due to the fact that the rapidly increasing size of the clerestory made such an addition to the lighting equipment unnecessary, though it is more probable that the great height of many of the churches rendered the construction of a tower over the crossing a dangerous undertaking. Even in the less lofty churches of England, where a central tower is almost invariably found, the latter is frequently closed from below by a vault. RIB-VAULTED CROSSINGS WITH NO LANTERNS [Illustration: FIG. 60.--LAON, CATHEDRAL.]