As the building has undergone extensive repairs since it became a mosque, care must be taken to distinguish between the original features of the fabric and Turkish changes and restorations. The pointed dome arches rest on pilasters built against the internal angles of the cross. The dome is windowless, has no internal drum, and externally is octagonal with a low drum and a flat cornice. Dome, arches, and pilasters are all evidently Turkish reconstructions. The gable walls of the transepts and the western wall are also Turkish. As the central apse coincided with the orientation of the mosque, it has retained its original form and some portions of its Byzantine walls, but it also has suffered Turkish alterations. The cross arches in the south gallery and in the narthex are pointed, and, in their present form, unquestionably Turkish; but as the vault above them is Byzantine, their form may be due to cutting away in order to secure a freer passage round the galleries for the convenience of Moslem worshippers. The outer narthex is Turkish, but the old wall which forms its foundation and traces of an old pavement imply the former existence of a Byzantine narthex. In spite, however, of these serious changes the building preserves its original characteristic features, and is a good example of a domed-cross church, with galleries on three sides and domes over the four angle-chambers. The galleries rest on a triple arcade supported by square piers. On the north and south the aisles are covered with cross-groined vaults on oblong compartments, while the passage or narthex under the western gallery has a barrel vault. The chambers at the north-eastern and south-eastern angles of the cross are thrown into the side chapels, which thus consist of two bays covered with cross-groined vaults. Communication between the chapels and the bema was maintained by passages opening in the ordinary fashion into the eastern bays. In the thickness of each of the eastern dome piers, and at a short distance above the floor, is a small chamber. The chamber in the north-eastern pier is lighted by a small opening looking southwards, and was reached by a door in the east side of the passage leading from the bema to the north-eastern chapel. The door has been walled up, and the chamber is consequently inaccessible. The chamber in the south-eastern pier is lighted by a window looking northwards, and has a door in the east side of the passage from the bema to the south-eastern chapel.