But, if we except perhaps Laval, nowhere shall we find the new system of vaulting upon intersecting arches more mightily demonstrated than at Angers, the aisles of which measure 54 feet across. The grandeur of the architectural composition, no less than the admirable technical skill shown in the details, gives proof of the consummate mastery arrived at by the builders of these noble structures so early as the middle of the twelfth century. The plan of these churches resembles that of Angoulême and Fontevrault. It is in no way allied to the Northern buildings. [Illustration: 11. PLAN OF A BAY OF THE NAVE IN THE CHURCH OF LA STE. TRINITÉ AT LAVAL] They are constructed with single aisles, like the cupola churches, with a series of bays, square on plan; but the arrangement of the vaults has been perfected by the logical use of intersecting arches in the place of pendentives, the architects of the day having realised by this time the progress we have explained and demonstrated in the preceding chapter. These vast aisles, vaulted on intersecting arches, are of course allied to the cupolas; they recall their general outline, but the arrangement of the vaulting is different. The intersecting ribs are no longer merely decorative features; they have taken on all the active functions of the _arc-doubleau_ and the formeret. Their union constitutes an elastic ossature, the weight being concentrated upon four points of support, which receive the impost of the arches, and compose a stone skeleton, each unit of which has been cut and dressed to fill the exact place it occupies in the whole. [Illustration: 12. LONGITUDINAL SECTION OF TWO BAYS IN THE NAVE OF LA STE. TRINITÉ AT LAVAL] If we compare the sections (Figs. 13 and 14) of the churches of Angoulême and Angers, we may clearly trace the filiation between these buildings, the one dating from the first years of the twelfth century, the other from some thirty or even forty years later. We shall also note the advance made by the Angevin architects in the construction of groined vaults in the place of domes with pendentives, a development worked out by the more perfect and reasoned application of the same architectural principle. [Illustration: 13 AND 14. COMPARATIVE SECTIONS OF THE CHURCHES OF ANGOULÊME AND ANGERS] [Illustration: 15. VIEW IN PERSPECTIVE OF THE NAVE VAULT OF ST. MAURICE AT ANGERS] The Church of Laval, built simultaneously with that of Angers, or only a few years later, shows a further advance, not merely in the matter of form, but in the increased science and ingenuity of combinations, and the methodical accuracy of the execution. [Illustration: 16. PLAN OF A SUMMER OF THE NAVE VAULT OF LA STE. TRINITÉ AT LAVAL] [Illustration: 17. PLAN OF ONE OF THE PIERS OF THE NAVE OF LA STE. TRINITÉ AT LAVAL]