This arrangement protects the vault from any infiltration of water due to the rupture of the tiles, an absolutely necessary precaution, if the former was to retain its stability. [Illustration: 70. ALBI CATHEDRAL. PLAN] [Illustration: 71. ALBI CATHEDRAL. SECTION OF THE NAVE] The Cathedral of Ste. Cécile at Albi is a monumental type of the single-aisled system. It is one of the largest and most important of Southern buildings constructed on the traditional principles of the ancient Romans. The vast single aisle, some 60 feet wide, is built entirely of brick, with the exception of the window tracery, the choir screen, and the south porch. Here we may study constructive principles no less simple than sagacious, combining all the necessary conditions of stability. The points of support and abutments of the vault on intersecting arches are all enclosed by the outer wall; they are thus protected from the accidents of climate, and their durability is almost indefinitely assured. [Illustration: 72. ALBI CATHEDRAL. APSE] [Illustration: 73. ALBI CATHEDRAL. DONJON TOWER AND SOUTH FRONT] The foundations of the cathedral, which was dedicated to St. Cecilia, were laid in 1282, on the ruins of the ancient Church of Ste. Croix. The main building was finished towards the close of the fourteenth century, and the whole as it now stands was completed in the last years of the fifteenth and early part of the sixteenth century, by the addition of the baldacchino of the southern porch, or principal entrance, of the stone rood loft, and choir screen, the stalls of carved wood, and the fresco decorations which adorn the whole building. This varied workmanship renders Albi one of the most instructive of studies in connection with French decorative art, the successive developments being marked by monumental examples of the highest order, inspired or created by divers influences. The architecture is of the Southern French type, as far as the main building is concerned; in essentials, the same type prevails in the magnificent porch known as the _baldaquin_, in the choir screen, and in the rood loft; but in these later additions the inspiration of Northern art at the close of the fifteenth and beginning of the sixteenth century is also perceptible. The statuary and sculptured ornaments of wood and stone are Flemish; the paintings indicate their Italian origin by their crudity of colour and vulgarity of motive. The Cathedral of Albi has a special interest as being one of the most curious examples of Southern Gothic architecture in the fourteenth century. It has a further peculiarity, inasmuch as it was not only a church, as it still is, but a fortress. Such a combination is readily accounted for by a study of the epoch following on the fierce struggle which ended in the extermination of the Albigenses, and of the social and political events resulting therefrom.