Lectures on the rise and development of medieval architecture; vol. 1

by Sir George Gilbert Scott

Fig. 10.

While these perplexities, however, were under consideration, several others arose, every one of which led to the introduction of features essential to the perfecting both of the style and construction. The first was the desire to elevate the central vault to a higher level, both for the sake of compensating for the loss sustained when it was brought down below the roof, and also to obtain a greater space for the clerestory windows. This involved, again, the difficulty as to abutment, through its raising the springing of the vault above the roof of the aisles. We have seen that, where reduced to a similar difficulty with the barrel vault, the architects of the south of France had at an earlier period resorted to the pointed vault as having less outward thrust: the same expedient was now had recourse to for groined vaulting, the main arches of which were now—towards the middle of the twelfth century—changed from the semicircle to the pointed arch. When the elevation of the clerestory above the aisles was but moderate, this was often found sufficient; but the construction was precarious, and in many instances failed, and a more perfect mode of meeting the case was required.

What was demanded was the power to elevate the clerestory with the main vault to any reasonable height above the aisle, without endangering the stability of the structure.

Here the recollection of an earlier expedient came to the rescue. It will be remembered that the early barrel vaults were buttressed by half barrel vaults over the aisles, thus doing away with the clerestory. A continuous vault demanded a continuous abutment; but, now that the pressure was concentrated into detached planes, it became sufficient that the abutment also should be in those planes; and though the continuous semi-vault would do away with clerestory windows, detached semi-arches would have no such effect. The thought accordingly occurred of erecting the arc-doubleau of the old semi-vault in open air as a buttress to the main vault of the groined church; and hence that much-admired, and, of course, also much-depreciated feature—the flying buttress. The pressure being concentrated upon points, it became also necessary to fortify those points by attached buttresses of considerable projection, such as we henceforth find to have become a leading external characteristic of Mediæval structures. The wall, in fact (where the system was carried to its extreme limits), became a mere curtain, needed rather for enclosure than for strength, and capable of being pierced with windows to any required extent; a liberty which the contemporaneous development of stained glass caused to be unhesitatingly taken advantage of.

I must, however, return to the vaulting, having overstepped my chronology by not yet noticing another most important invention. I mean the introduction of groin-ribs—those narrow arches erected under the lines of intersection of the vaults. The early groins had no ribs excepting the transverse ones, or arcs-doubleaux; the edges at which the vaults cut one another were left bare, and were the weakest parts of the construction; often but faintly marked, and not necessarily lying in planes. In more complicated vaults, such as now became necessary, this system could scarcely be continued; and the introduction of a stone rib, under every intersection, may be viewed as the crowning fact in the development of vaulting.

It is impossible to lay too much stress upon its importance, for it changed the entire geometrical system. Up to that time the construction of groining was wholly governed by the forms of the vaulting surfaces; the intersections being allowed to take their chance, and to present any irregularity of figure, while the wide surfaces of vaulting were apparently carried on mere pins’ points at the springing—correct enough as a mathematical figure, but ill calculated for strength. Now, however, the intersecting lines assumed the government of the construction, and the form of the surface was made to accommodate itself to them. They were always in planes,[6] and always true figures—usually arcs of circles; but the panels of vaulting became often irregular in their configuration, and could be twisted to meet contingent requirements without offending the eye; while the ribs, all meeting in a solid springer at the foot, brought down the pressure, and deposited it firmly upon the points of support.

Fig. 11.

It will be seen from the above that the pointed arch was not introduced into Mediæval structures from mere caprice—merely from seeing it elsewhere and taking a fancy to its form,—but from the necessities of construction, from its increased strength and diminished thrust. It was at first used for the main arch only of the greater vault. The same reason soon led to its introduction wherever great weight was to be carried, as under towers, etc.; but for all small arches the semicircle was long retained. I have alluded to the very beautiful theory that it was introduced for the side arches of oblong groins, simply as a means of obtaining arches of equal height with only half the span with those of the main vault. True it is, that, at a later date, it became most useful for this purpose. But a careful study of the monuments in which it is first systematically used clearly shows that its introduction was from statical, and neither geometrical nor merely æsthetical motives; for in the face of that theory we find the narrower arch or wall-rib remaining round long after the wider arch had become pointed ([Fig. 11]). Such is the case in nearly all the earlier of the French transitional churches, as at Noyon and at St. Germain des Pres, and we see the same at Canterbury. In most of these buildings the narrow arch is stilted and the crown of the cross vault raised up as before described, thus losing a part of the clerestory wall, a disadvantage obviated when the pointed arch became more frankly acknowledged.