The altar itself, a name which insensibly became familiar to Christian ears, was placed in the eastern recess, artificially built in the form of a demi-cylinder; and this sanctuary communicated by several doors with the sacristy, the vestry, the baptistery, and the contiguous buildings, subservient either to the pomp of worship, or the private use of the ecclesiastical ministers.
The memory of past calamities inspired Justinian with a wise resolution, that no wood, except for the doors, should be admitted into the new edifice; and the choice of the materials was applied to the strength, the lightness, or the splendor of the respective parts.

The solid piles which contained the cupola were composed of huge blocks of freestone, hewn into squares and triangles, fortified by circles of iron, and firmly cemented by the infusion of lead and quicklime: but the weight of the cupola was diminished by the levity of its substance, which consists either of pumice-stone that floats in the water, or of bricks from the Isle of Rhodes, five times less ponderous than the ordinary sort.

The whole frame of the edifice was constructed of brick; but those base materials were concealed by a crust of marble; and the inside of St.
Sophia, the cupola, the two larger, and the six smaller, semi-domes, the walls, the hundred columns, and the pavement, delight even the eyes of Barbarians, with a rich and variegated picture.

A poet, [105] who beheld the primitive lustre of St.Sophia, enumerates the colors, the shades, and the spots of ten or twelve marbles, jaspers, and porphyries, which nature had profusely diversified, and which were blended and contrasted as it were by a skilful painter.

The triumph of Christ was adorned with the last spoils of Paganism, but the greater part of these costly stones was extracted from the quarries of Asia Minor, the isles and continent of Greece, Egypt, Africa, and Gaul.