More important by far, are the churches without side aisles but with naves in square bays with four part cross-ribbed vaults. This method is to be seen in the cathedral of Fréjus (Var),[158] which is considered by Porter[159] to exhibit the earliest extant ribbed nave vaults in France. These are distinctly of Lombard type, and would seem to show a strong Lombard influence entering France from the south. It may possibly be that this same influence followed the route taken earlier by the dome on pendentives, and thus gave rise to the domed up ribbed vault so common in the churches of Anjou.[160] Of these latter, the cathedral of Saint Maurice at Angers (Maine-et-Loire) (Fig. 19), presents perhaps the best existing example. Its nave vaults which date from as early as 1150[161] are among the largest and finest in France, having a span of some fifty-six feet. As in Lombardy, the crown is highly domed up while to facilitate the construction of the web of the vault with the least possible centering, pointed diagonals and enclosing arches are employed. By this means the entire vault was constructed on the ribs with no centering at all for the lower courses, and a simple _cerce_, a device consisting of two curved boards sliding along each other, for those near the crown. At the same time the outward thrusts were greatly reduced by the pointed section of the vault. ANJOU RIDGE RIBS FIG. 19.--ANGERS, CATHEDRAL. Since the Anjou churches possessed naves of wide span, it is not surprising to find that their builders soon added ridge ribs beneath the vault. That these were not mere cover-joints to conceal an irregular intersection of the masonry, as Choisy suggests,[162] would seem to be proved by the fact that the courses meet in a straight line at the ridge in by far the greater number of Anjou churches in which they are employed,--for example in La Couture at Le Mans (Fig. 20), Airaines,[163] and numerous churches with small torus ribs, as well as by the fact that such ridge ribs are sometimes omitted even when the masonry is laid up in courses of equal width and therefore interpenetrating at the ridge, as in Avesnières (Mayenne)[164] near Laval. If not, however, primarily a cover-joint, these ribs did at least possess both a structural and decorative quality. In the first place they helped to keep the keystone of the diagonals rigidly fixed during the building process, and furthermore, they gave an absolutely straight line to the vault crown which was always difficult to adjust, particularly in a vault of large size. One of the best and earliest examples of the employment of such ribs appears in the nave of Notre Dame-de-la-Couture at Le Mans (Fig. 20) which dates from about 1200, and a later example is afforded by the church of Saint-Avit-Sénieur (Dordogne),[165] where the vaults are of the thirteenth century and replace an original series of domes on pendentives of true Perigord type. [Illustration: FIG. 20.--LEMANS, NOTRE DAME-DE-LA-COUTURE.]