With the introduction of ribbed vaulting, examples of six-part vaults, four-part vaults of rectangular and square plan and many forms of complicated vaulting are to be found in the transept exactly as they have been in the nave. Only those vaults which are unusual in character will therefore be discussed. Of these the most important is the five-part rectangular vault sometimes used as a termination of the transept arm. From its appearance in Normandy, and its evident relation to sexpartite vaulting, this method may be assumed to have arisen there. The Abbaye-aux-Dames at Caen (early twelfth century) affords an example of such a vault. It was evidently employed to subdivide the end walls into bays similar to those in the remainder of the church, and thus provide a uniform elevation and window arrangement throughout the edifice. In spite of its uniformity the arrangement is an awkward one, for it brings a pier directly in the center of the transept wall where it would be more natural to find a door. The five-part vault did not, therefore, become a general method of transept termination, though there is a very fine example of its survival in the church of Saint Urbain at Troyes (Aube) (cir. 1262-1300). It may even be that the desire for a regular elevation of the bays led to the subdivision of the transept by a row of central piers, such as those in the large church at Saint Nicolas-du-Port (Meurthe-et-Moselle) (sixteenth century)[287] and in a number of smaller examples, some of them of earlier date.[288] SQUARE CHEVETS Such a vault as that just described was, in a way, a sort of square chevet.[289] It was built to provide a better arrangement of windows in the terminal wall than would be possible beneath the transverse cell of a regular four-or six-part vault. Nor was its use confined to the transept for it is found with a varying number of cells at the end of the nave and choir as well. Such Norman churches as Saint Georges at Saint Martin-de-Boscherville (Fig. 51), Saint Étienne at Caen and Saint Cross at Winchester (choir cir. 1135-1189) are examples of this,[290] while the vaults of the transepts of Limburg Cathedral[291] (1235) and that of the chapter house at Boscherville (Fig. 52) resemble a chevet even more closely in that all but one of their severies are subdivided. When the ribs all rise from the same level, the appearance of such a vault is pleasing, but when,--as in the nave of Boscherville (Fig. 51),[292]--the intermediate ribs are shortened, [Illustration: FIG. 51.--SAINT MARTIN-DE-BOSCHERVILLE, SAINT GEORGES.] [Illustration: FIG. 52.--SAINT MARTIN-DE-BOSCHERVILLE, SAINT GEORGES, CHAPTER-HOUSE.] the effect is very unsatisfactory, though this shortening of the ribs probably had a structural advantage in preventing the light from being partly cut off, or the windows partly concealed by the radiants and the masonry above them. VAULTING OF SEMICIRCULAR TRANSEPTS