CHAPTER V

ORIGIN OF THE FLYING BUTTRESS

The primitive method of vaulting adopted in the central provinces of France in the construction of churches with three aisles rendered such buildings of necessity low and heavy. The main aisle being covered by a barrel vault, supported on either side by a continuous half-barrel vault, the sole means of lighting lay in the windows of the side aisles, so that the nave was always gloomy in the extreme. The Norman architects had avoided this difficulty, first in their native province, and afterwards in England, by vaulting the subordinate aisles only, and by raising the lateral walls of the nave high enough to allow a line of windows to be introduced between the lean-to roofs of the side aisles and the nave roof, the latter being an open timber construction instead of a vault.

The lateral gallery in the first story of Norman churches built on the basilican model is merely a development of the ancient tradition.[6] It bears the name of triforium because--or so we are told--each compartment of such an interior gallery between the main piers of the nave was originally divided into three by pillars supporting lintels or by small columns supporting an arcade.

[6] See _L'Architecture Romane_, by Ed. Corroyer; Maison Quantin, Paris, 1888, chaps. i. iii. and iv.

Towards the close of the eleventh century Norman architects on both sides of the Channel were raising vast churches, the side aisles of which bore above their ribbed vaults galleries after the fashion of the primitive basilicas. These galleries in their turn were covered by open timber roofs like that of the nave. The bays were emphasised in the nave and in the side aisles by transverse arches, or _arcs-doubleaux_, which served as buttresses to those of the main vault. But after the adoption, towards the middle of the twelfth century, of the Angevin method of vaulting for religious buildings, the functions of the lateral walls and of the supporting arches became better defined, for these walls and arches had now to meet the thrusts of the transverse as well as that of the diagonal arches, which, meeting in bundles, as it were, at each pier, gathered their energies at well-marked points.

It was thus that the cross walls or _arcs-doubleaux_ of the side aisles were gradually modified till they became detached semi-arches concealed beneath the outer roof of the side aisles.

We have traced this modification in the Abbaye aux Dames at Caen.[7]

[7] _L'Architecture Romane_, by Ed. Corroyer; Paris, Maison Quantin, 88, chap. xvii.

Fig. 24 shows us an English example. It may be followed out in a number of other churches in England, at Pavia in Italy, at Zurich in Switzerland, and at Basle on the Rhine, to name but a few of the churches in which the modification of the vaults was long posterior to the construction of the building itself.

In France we shall find no example more deeply interesting than Noyon, which at the date of its construction (the last quarter of the twelfth century) formed, as it were, an epitome of the advance so far made by the architects of the Ile-de-France. In this curious building we find a fusion of the antique tradition developed by the Normans in their triforiums, and of the Angevin methods, as manifested in the groined vaults derived from domes: methods further perfected by the example of La Ste. Trinité at Angers; in other words, by the adoption of intersecting arches planned on a square, the thrusts of all being received on the main piers, reinforced by an intermediate transverse arch. And we note the appearance of the detached semi-arch beneath the roofing of the inferior aisles merging at its springing into the lateral _arc-doubleau_, and so resisting the thrust of the intersecting arches and transverse arches of the nave.

It has been said that Noyon was suggested by Tournai, doubtless on account of their superficial affinities. But the likeness is merely in general aspect, the methods of construction being wholly different. At Tournai the apsidal transepts are vaulted upon transverse arches of great strength, and upon radiating semi-arches united where they meet by a ring of voussoirs set horizontally, and at their springing by vaults keyed into their mass, an ingenious arrangement which recalls the vaulting of the _Salle des Capitaines_ over the porch of the monastery church at Moissac.

The combination of these _arcs-doubleaux_, which, in addition to the solidity of their independent structure, are strongly reinforced by the massive circular courses of the walls, is very peculiar, for it dispenses altogether both with auxiliary arches and with abutments. Tournai, therefore, cannot be held to have begotten Noyon, for here we have groined vaults, the intersecting arches of which demand the reinforcement of abutments either concealed or apparent to sustain the thrust of these vaults over the lateral _arcs-doubleaux_. The ingenious arrangement above cited had in no sense modified the methods of abutment followed by the architects of the twelfth century even after the adoption of the vault on intersecting arches. These, as will be remembered, consisted in buttressing the walls and piers of the nave by cross walls or by arches concealed beneath the roofing of the side aisles.

We find at Soissons the first application of an architectural system, the special feature of which is the _flying buttress_.

The south transept of Soissons Cathedral was evidently suggested by Noyon. This is apparent in the adoption of the two-storied side aisle and in the semi-circular plan. But the method of vaulting common to both churches has a greater refinement at Soissons. Reduced to its simplest expression of strength by the attenuation of its skeleton, the vault still exercises its full thrust on those parts which rise above the upper gallery.

The architect of Soissons was not content, like his brother of Noyon, to support the vault laterally by interior arches collaborating with the _arcs-doubleaux_ of the triforium, and reinforced by an abutment impinging on the wall of the central nave. To him the idea occurred of detached semi-arches in open air, springing from above the roof of the triforium and its buttresses and marking each bay. Thus was born the _flying buttress_, a feature frankly emphasising its special aim and function, namely, to meet the thrust of the main vault at its points of concentration.

[8] These flying buttresses, in themselves insufficient for the task laid upon them, and worn by the destructive action of the weather, were pushed entirely out of shape by the constant pressure from within, the thrust of the vault being aggravated by the circular plan of the building, while the vaults themselves became dislocated by reason of their insufficient abutments. It became necessary to reconstruct the buttresses in 1880, to avert the total collapse of the south transept.

The reconstruction of these flying buttresses, and of many others of the same period, furnishes us with a criticism _ad hominem_ upon the system.

The flying buttress, in combination with the intersecting arch, gave birth to a new system of construction, a system on which were raised vast buildings which compel our admiration and demand our careful study, but should not invite our imitation. They are monuments to the ingenuity of the twelfth and thirteenth century architect, but no less are they beacons warning against the perils of a rationalism--more apparent than real--which their authors carried to its extreme limits, casting to the winds all traditional principles, and consequently all authority.

It would seem as though the architects of this period, emboldened by such achievements as the churches of Noyon, Soissons, Laon, Paris, Sens, and Bourges, and spurred by professional emulation, went on from one feat of daring to another, passing from the triumphs of Rheims, Amiens, and Mans to the supreme architectural folly of Beauvais, and creating monuments no less amazing in dimension than in the statical problems grappled with, if not always solved.