No bolder idea was ever introduced in constructive architecture; for now the dome, instead of being, as at the Pantheon, supported firmly by a solid wall throughout _every_ portion of its circumference, finds its conditions _absolutely reversed_; for in _no_ portion of its circumference has it now a solid support, but all floats upon vacuity, suggesting the poetical similitude to Procopius that the Dome of St. Sophia appeared as if suspended by a chain from heaven. Pendentive domes, in neither of their typical forms, seem to have been frequently or customarily made use of in the more genuine Classic ages, though in modern times they have both been very wisely adopted into the revived Classic styles. They were, in fact, the special characteristic and the great glory of the Byzantine style. Mr. Freeman, on this subject, remarks:--“The offspring of the arch is the vault, of the vault the cupola; and this majestic ornament is the very life and soul of Byzantine architecture, to which every other feature is subordinate. Its use had hitherto been mainly confined to circular buildings. To make it the central point of a Christian temple was a grand and bold idea, and one which involved a complete revolution in the existing principles of architecture.... And not only did the grand cupola crown the whole pile, but the smaller portions are often covered with smaller domes and semi-domes.... The eye, habituated to the long naves ... of our own great churches, is totally bewildered with so huge a pile, with apses and semi-domes ‘sprouting out,’ to use the expression of Mr. Hope, in every direction, and all circling round the vast central cupola, like tributary rulers encircling an imperial throne.” It is thought by some that the Byzantines borrowed the pendentive dome from Persia, but this seems insusceptible of proof; indeed, it exists of earlier age in Italy. It is more certain that having once discovered its wonderful utility, it was communicated by them to every region to which their influence extended, and that, having been learned from them by the Mahometans, it became the conspicuous feature of the architecture which extended continuously from the Bay of Bengal to the Atlantic. The next development I will mention is the raising of the dome proper upon a drum or circular wall, elevated upon the pendentives or corbels, so as to convert it into a species of tower. This seems to have been the first step by which, in later times, the dome came to be made a conspicuous external feature, though rather at the sacrifice of internal beauty (Figs. 416, 417). [Illustration: Fig. 416.] [Illustration: Fig. 417.]