On the exterior the eastern wall of the church is fairly well preserved. The three apses project boldly; the central apse in seven sides, the lateral apses in three sides. Although the central apse is unquestionably a piece of Byzantine work it does not appear to be the original apse of the building, but a substitute inserted in the course of repairs before the Turkish conquest. This accounts for its plain appearance as compared with the lateral apses, which are decorated with four tiers of five niches, corresponding to the window height and the vaulting-level within the church. As on the apses of the Pantokrator (p. 235) the niches are shallow segments in plan, set back in one brick order, and without impost moulding. In the lowest tier three arches are introduced between pilasters, with a window in the central arch. Above the four tiers of niches is a boldly corbelled cornice, like that in the chapel attached to the Pammakaristos. One cannot help admiring how an effect so decidedly rich and beautiful was produced by very simple means. [Illustration: PLATE XLV. (1) S. THEODOSIA. DOME OVER THE STAIRCASE TO THE GALLERIES. (2) S. THEODOSIA. THE NARTHEX, LOOKING NORTH. _To face page 172._] Details of the tiled floor and of several carved fragments are given in Fig. 76. For some time after the conquest the building was used as a naval store.[283] It was converted into a mosque in the reign of Sultan Selim II. (1566-74) by a wealthy courtier, Hassan Pasha, and was known as Hassan Pasha Mesjedi.[284] Its title, the mosque of the Rose, doubtless refers to its beauty, just as another mosque is, for a similar reason, styled Laleli Jamissi, the mosque of the Tulip.