 The arches, four in number, rise aloft and are bound together in the same manner and the circular drum which stands upon them is pierced by windows, and the dome which arches above this seems to float in the air and not to rest upon solid masonry, though actually it is well supported.Thus, then, was the central part of the roof constructed.And the arms of the building, which are four... were roofed on the same plan as the central portion, but this one feature is lacking