In addition to the western entrance, a door on the north, now blocked up, led through an open porch into a small court. The large cylindrical arch of this porch had a screen at its northern side, the columns and door-frame[245] of which are still extant, but the marble lattice is destroyed. Through an arch in the east wall of this porch the addition which was made outside the south-west buttress pier could be reached, where there was a passage into the church. Salzenberg’s plan[246] of this addition is taken at the level of a landing reached by a staircase from the passage through the south-west buttress pier. This landing seems at one time to have been connected with a chamber above the north porch of the baptistery, and from thence with the stairway at the south-west angle of the church. Leading upwards from this landing is the original staircase to the gynaeceum, and at this level there is a small chapel vaulted with a cupola.[247] The vault is adorned with mosaic; figures of angels stand in the four pendentives. Originally the chapel was not lighted; but at the last “restoration” a hole was made in the roof, which was filled with glass; a passage from this chapel to the gynaeceum is probably Turkish. The chapel is supposed by the Greeks to be the one into which the officiating priest disappeared at the capture by the Turks. The Turks turned the baptistery into a storeroom for the oil used in lighting the church, but on the sudden death of the Sultan Mustapha I. it was converted into a turbeh. Almost the whole of the church is raised above vaulted cisterns. An opening in the south aisle[248] gives access to the water, and there is another opening in the north-west exedra. The depth of the water prevented a close inspection. Of the two additions made in Byzantine times to the centre of the north and south walls on the outside, and intended to buttress the aisles, the southern one has been further lengthened by the Turks. To preserve the use of the door and window in the wall of the church, each addition was pierced by a passage. Remains of stairways and side passages have also been found here.[249] Other remains of buildings existed on the north and south sides of the church, but they were too insufficient to base any conclusions on them. _Materials._--The principal materials employed are brick, and a kind of peperino stone. The latter is used in those parts of the building which have to stand great pressure, such as the four large piers in the nave, the piers to east and west, and the extra projections from the buttress piers in the side aisles and gynaeceum. In addition a horizontal course two feet deep runs round the whole building four feet from the floor. The outside walls of the original building, like the vaulting, were entirely of brick, but in the later additions they are formed of alternate layers of brick and stone, and some of the later buttress masses are almost entirely of stone.