=Domes.=--The roofs are flat, constructed of timber, and on the inside coloured and gilded. A dome frequently crowns the _maksura_ or prayer chamber, and the tomb of the saint, when the latter is included in the sacred precincts. Almost always the dome surmounts a square plan and to accommodate the latter to the circle the Muhammedan architects invented a method of construction that corresponds to the Byzantine pendentive. In principle it goes back to the ancient method of bridging over a space by setting the stones on each side of it in layers that project over one another until the two sides meet at the top. The Muhammedan builders filled in the corners of the square with tiers of projecting brackets or corbels with niches between them. At first they placed corbel above corbel and niche above niche, but in time alternated them, so that the niches in one tier were astride of the corbels in the tier below them. This method of filling in the angles of the square, so as to bring the latter to a circle, came to be known as “stalactite” work and from being used as a constructive expedient was developed into a system of decoration that was frequently extended over the whole ceiling of the vault. The exterior of the dome was seldom spherical, as in Byzantine architecture, but took the form of the _pointed_, or the _ogee_, or the _horseshoe_ arch. It was built, either of brickwork in horizontal courses, covered inside and out with plaster; or, in later mosques, of horizontal layers of stone, engraved on the exterior with horizontal patterns. Windows were frequently ranged round the lower part. In some old tombs of the thirteenth century, as that of =Sheik Omar=, inside the East Gate of Bagdad, the dome is pineapple shaped. The walls were built of local materials and decorated either with stone or brick in alternate courses, or with plaster, inset with precious stones or veneered with glazed tiles. =Minarets.=--A distinctive feature of the mosque was the minaret, a lofty tower of lighthouse form, from the balcony of which the muezzin summoned the faithful to prayer. While the minarets show a general similarity of character, the details vary in different countries. Thus, in Persia they rise from a circular base and are crowned by a round cap; in Constantinople the base is round, octagonal, or square and the top is finished with a cone; while in Cairo the top is flat. The shafts vary from circular to polygonal, and are usually divided into three tiers of balconies--though the Persian is generally distinguished by one--carried round the shaft and supported by corbels, which in some instance are embellished with stalactite ornament.