The works of the Angevin architects were of course known to their Northern brethren, who, in common with all the builders of the day, had long been seeking the final solution of the great problem of the vault. The architects of the Ile-de-France at once appropriated the Angevin system with that special professional ingenuity which characterised them, and applied it to the construction of innumerable churches, large and small, all of them built on the basilican plan--that is to say, with three, or even five aisles. Thus the Aquitainian cupola of dressed stone exercised an absolutely direct influence upon Gothic architecture, since it gave birth to the _intersecting arch_, which is the main feature of so-called Gothic. This influence was first manifested in the general arrangement of single-aisled churches vaulted upon intersecting ribs, the earliest departure from the original cupola. It was then more grandiosely demonstrated in vast abbey or cathedral churches, built in accordance with the basilican tradition, and all vaulted on the new principle. Angers and Laval are primitive examples of churches whose square compartments carry groined vaults, which thenceforth took the place of cupolas with pendentives. The abbey church of Noyon shows the application of this principle, novel in the twelfth century, to the several-aisled churches of the Northern architects. The _original_ vaults of Noyon[4] were planned in square. The intersecting arches united the principal piers diagonally, the strain being relieved by a subordinate or auxiliary arch which rested upon secondary piers, indicated on the exterior by buttresses less salient than those of the main piers, and on the interior by a column receiving the lateral archivolts which united the chief piers. [4] The original disposition of the vaults built about 1160 is indicated by the spring of the arches above the capitals, and by the base plan of the principal piers. The present vaults on rectangular plan were built after the fire of 1238, in accordance with prevailing fashions. This system of construction, the principle of which was logically developed at Noyon, for instance, no longer exists, save in its traditional state in the great churches of Laon, and in the cathedrals of Paris, Sens, and Bourges, to name but the principal, without regard to the innumerable churches built on these principles throughout Western Europe. In these great buildings the vaults were all square on plan down to the adoption in the first half of the thirteenth century of equal bays, vaulted on a rectangular plan, and marked inside and out by equal piers and projections, as at Amiens, Rheims, and many other churches of the period.