The section across the nave (Woodcut 553) shows the form of the central vault, which the longitudinal section shows to be a plain tunnel-vault unbroken by any intersection throughout the whole length of the nave. The side aisles are roofed with half vaults, forming abutments to the central arches—the advantage of this construction being, as before explained, that the tiles or paving-stones of the roof rest directly on the vault without the intervention of any carpentry. Internally also the building displays much elegant simplicity and constructive propriety. Its chief defect is the darkness of the vault from the absence of a clerestory, which though tolerable in the bright sunshine of the South, could not be borne in the more gloomy North. It was to correct this, as we shall afterwards perceive, that in the North the roof of the aisles was first raised to the height of that of the central nave, light being admitted through a gallery. Next the upper roof the aisles was cut away, with the exception of mere strips or ribs left as flying buttresses. Lastly, the central vault was cut up by intersections, so as to obtain space for windows to the very height of the ridge. It was this last expedient that necessitated the adoption of the pointed-headed window. It might never have been introduced but for the invention of painted glass, but this requiring larger openings, compelled the architects to bring these windows close up to the lines of the constructive vaulting, and so follow its forms. In the South, however, painted glass never was, at least in the age of which we are now speaking, a favourite mode of decoration, and the windows remained so small as never to approach or interfere in any way with the lines of the vault, and they therefore retained their national and more beautiful circular-headed termination. The modes of introducing light are, however, undoubtedly the most defective part of the arrangements of the Provençal churches, and have given rise to its being called a “cavern-like Gothic”[24] from the gloom of their interiors as compared with the glass walls of their Northern rivals. Still it by no means follows that this was an inherent characteristic of the style, which could not have been remedied by further experience; but it is probable that no ingenuity would ever have enabled this style to display these enormous surfaces of painted glass, the introduction of which was, if not the only, at least the principal motive of all those changes which took place in the Frankish provinces. [Illustration: 554. Doorway in Church at Maguelonne. (From Renouvier, ‘Monuments de Bas Languedoc.’)]