The splendid mosque of +Ibn Touloun+ (876-885) was built on the same plan as that of Amrou, but with cantoned piers instead of columns and a corresponding increase in variety of perspective and richness of effect. With the incoming of the Fatimite dynasty, however, and the foundation of the present city of Cairo (971), vaulting began to take the place of wooden ceilings, and then appeared the germs of those extraordinary applications of geometry to decorative design which were henceforth to be the most striking feature of Arabic ornament. Under the Ayûb dynasty, which began with Salâh-ed-din (Saladin) in 1172, these elements, of which the great +Barkouk+ mosque (1149) is the most imposing early example, developed slowly in the domical tombs of the _Karafah_ at Cairo, and prepared the way for the increasing richness and splendor of a long series of mosques, among which those of +Kalaoun+ (1284-1318), +Sultan Hassan+ (1356), +El Mu’ayyad+ (1415), and +Kaîd Bey+ (1463), were the most conspicuous examples (Fig. 80). They mark, indeed, successive advances in complexity of planning, ingenuity of construction, and elegance of decoration. Together they constitute an epoch in Arabic architecture, which coincides closely with the development of Gothic vaulted architecture in Europe, both in the stages and the duration of its advances. The mosques of these three centuries are, like the mediæval monasteries, impressive aggregations of buildings of various sorts about a central court of ablutions. The tomb of the founder, residences for the _imams_, or priests, schools (_madrassah_), and hospitals (_mâristân_) rival in importance the prayer-chamber. This last is, however, the real focus of interest and splendor; in some cases, as in Sultan Hassan, it is a simple barrel-vaulted chamber open to the court; in others an oblong arcaded hall with many small domes; or again, a square hall covered with a high pointed dome on pendentives of intricately beautiful stalactite-work (see below). The ceremonial requirements of the mosque were simple. The-court must have its fountain of ablutions in the centre. The prayer-hall, or mosque proper, must have its _mihrâb_, or niche, to indicate the _kibleh_, the direction of Mecca; and its _mimber_, or high, slender pulpit for the reading of the Kôran. These were the only absolutely indispensable features of a mosque, but as early as the ninth century the _minaret_ was added, from which the call to prayer could be sounded over the city by the _mueddin_. Not until the Ayubite period, however, did it begin to assume those forms of varied and picturesque grace which lend to Cairo so much of its architectural charm.