With these beautiful details the rich treasure-trove of the interior is exhausted, and one passes out to study the details of the exterior. The Cathedral's single tower, which rises behind the facade line, was one of the parts that was longest neglected,--perhaps because a tower is less essential to the ritual than any other portion of an ecclesiastical building. Begun in 1323, the work dragged along with many periods of absolute idleness, until 1880, when a balustrade with pinnacles at each angle was added to the upper octagonal stage, and the building of the tower was thus ended. The octagon with its narrow windows rests on a plain, square base that is massively buttressed. It is a pleasant, rather than a remarkable tower, and one's eye wanders to the more beautiful facade. Here, encased by severely plain supports, is one of the most charming portals of Provencal Gothic. Decorated buttresses stand on either side of a large, shallow recess which has a high and pointed arch, and in the centre, a slim pier divides the entrance-way into two parts, pre-figuring the final division of the Just and the Unjust. A multitude of finely sculptured statues were formerly hidden in niches, under graceful canopies, and in the hundred little nooks and corners which lurk about true Gothic portals. Standing Apostles and seated Patriarchs, baby cherubs peering out, and the more dramatic composition of the tympanum--the Transfiguration,--all lent a dignity and wealth to Saint-Sauveur. Unfortunately many of these sculptures were torn from their crannies in the great Revolution; and it is only a few of the heavenly hosts,--the gracious Madonna, Saint Michael, and the Prophets,--that remain as types of those that were so wantonly destroyed. The low, empty gables that sheltered lost statues, their slender, tapering turrets, and the delicate outer curve of the arch, are of admirable, if not imposing, composition. The portal's wooden doors, protected by plain casings, abound in carvings partly Renaissance, partly Gothic. The Sibyls and Prophets stand under canopies, surrounded by foliage, fruits, and flowers, or isolated from each other by little buttresses or pilasters. This Gothic portal quite outshines, in its graceful elaboration, the smaller door which stands near it, in the simpler and not less potent charm of the Romanesque. And side by side, these portals offer a curiously interesting comparison of the essential differences and qualities of their two great styles. If the Romanesque of Saint-Sauveur is far surpassed at Arles and Digne and Sisteron, nowhere in Provence has Gothic richer details; and if the noblest of Provencal creations must be sought in other little cities, the lover of architectural comparisons, of details, of the many lesser things rather than of the harmony of a single whole, will linger long in Aix. [Illustration: THE CATHEDRAL.--AIX.]