§ 1. BUILDING PROCEDURE.
The method and sequence of the building operations as followed by the Byzantines seem to have been very much as follows. After the form of the building had been more or less decided, the first thing necessary was to collect marble monolithic shafts. At S. Sophia the eight verde-antique shafts match one another very closely; they are all of one length, and vary from 7½ to 8 diameters in proportion. The four pairs of porphyry shafts in the exedras differ much more; and, as we have remarked, those in the western exedras seem to be made up of separate drums. The proportions of these vary from less than 7 diameters on one side to 8½ on the other. The great monoliths are the largest known, and of nearly normal classic proportion, so we can readily see that it was necessary to have a certain knowledge where such marbles might be quarried or otherwise obtained, before even the foundations were prepared, for the columns decided the heights and points of support of the building. These once assured, the body of the structure was proceeded with as a brickwork shell without further dependence on the masons, who were only required to prepare bases and capitals, and then the cornices; everything else was completed as a brick “carcase.”
At S. Sophia the main square piers are in fact stone, but this was only for strength, not because they were to be seen finally, any more than the rough brick.
The building completed in this form we must remember was made up of vast masses of thin bricks, of which the mortar occupied probably a half of the aggregate; this had to thoroughly settle down and dry before the rest of the marble masonry was inserted, and the wall casings applied. The marble work, however, was all the while being prepared, and, the building once ready, the windows were inserted as screens in the openings previously left; marble jambs and lintels for the doors were placed in position also, with windows above them filling out to the brick arches. The walls were then sheeted with their marble covering, the vaults were overlaid with mosaic, and the pavement was laid down. In this way, as the bricklayers had not to wait for the masons, the carcase was completed in the shortest possible time; and by reserving the application of the marble until the structure was dry and solid, it was possible to bring together unyielding marble and brickwork that must have settled down very considerably.