The walls above gallery level and the large vaulting surfaces of the building are now covered with plaster, but a close examination proves that if any mosaic or marble revetment ever existed above gallery level, none of it, excepting the mosaic in the apse, remains.
Looking next at the exterior of the building, it is to be observed that the ground on the north, south, and east has been raised as much as fifteen feet. In many places the walls have undergone Turkish repair. The apse shows three sides. The drum of the dome is pierced by twenty semicircular-headed windows (of which only five are now open), and as their arches and the dome spring at about the same level the heads of the windows impinge upon the dome's surface. Two low shoulders cover the eastern pendentives. The plan of the drum is peculiar. From the shoulders, just mentioned, to the windows, it is a square with rounded corners, one side of the square being joined with and buried in the drum of the western dome vault; but upon reaching the base of the windows it becomes an accurate circle in plan, and at the springing of the window arches is set back, leaving a portion of the piers to appear as buttresses. The upper portion of the drum is carried well up above the springing of the dome, leaving a large mass of material properly disposed so as to take the thrusts produced.
The careful examination of the building by Mr. George has proved that the fabric is not the work of one age, but consists of parts constructed at different periods. For the full evidence on the subject we must await the forthcoming monograph on the church. Here, only the main results of Mr. George's survey can be presented.
Up to the level of the springing of the aisle vaults, the walls of the main body of the building, excepting the narthex and the additions at the east end of the church, are built of large well-squared stones laid in regular courses, and are homogeneous throughout.
Above that level the walls are built in alternate bands of brick and stone, five courses of brick to five courses of stone being the normal arrangement. The stones in this portion of the walls are smaller and much more roughly squared than those below the springing of the aisle vaults. This brick and stone walling is, so far as could be ascertained, homogeneous right up to the domical vault and the dome. As usual the arches and vaults are in brick. A point to be noted is that the recesses or openings in the lower part of the north and south walls of the church do not centre with the windows and vaulting above them; sometimes, indeed, the head of an opening comes immediately below a vaulting arch or rib. Again, at the north-eastern external angle of the apse the wall up to the level of the springing of the aisle vaulting is in stone, but above that level in brick, and the two portions differ in the angle which they subtend. Evidently there has been rebuilding from a level coinciding with the springing of the aisle vaulting. Projecting above the ground at the same place is a square mass of stonework that was left unbuilt upon when that rebuilding took place. The narthex is built of brick, with bands of large stone at wide intervals, and is separated by distinct joints from the upper and lower walls of the body of the church. Furthermore, while the two eastern bays on each side of the western portion of the nave continue and belong to the unusual system of vaulting followed in the aisles, the bay on each side immediately adjoining the narthex belongs to the vaulting system found in the narthex, and has, towards the nave, an arch precisely similar to the arches between the nave and the narthex. The division between the two systems is well marked, both in the nave and in the aisles, and points clearly to the fact that the narthex and the body of the church are of different dates.
S. Irene.
Vaulting Over the South Aisle.
S. Irene.
A Compartment of South Aisle Vaulting
(looking directly upward).