Although the building is now almost a complete ruin, it still preserves some architectural interest. On the exterior it is an octagonal structure, with a large arch on each side rising to the cornice, and thus presents a strong likeness to the Byzantine building known as Sheik Suleiman Mesjedi, near the Pantokrator (p. 25). The northern, southern, and western arches are pierced by windows. The entrance is in the western arch. The interior presents the form of an equal-armed cross, the arms being deep recesses covered with semicircular vaults. The dome over the central area has fallen in. The apse, semicircular within and showing five sides on the exterior, is attached to the eastern arm. Its three central sides are occupied by a triple-shafted window. Two shallow niches represent the usual apsidal chambers. A similar niche is found also on both sides of the entrance and on the eastern side of the northern arm of the cross. In the wall to the west of the southern arch is a small chamber. The joint between the apse and the body of the building is straight, with no bond in the masonry; nor is the masonry of the two parts of the same character. In the former it is in alternate courses of brick and stone, while in the latter we find many brick courses and only an occasional stone band. Evidently the apse is a later addition. In view of these facts, the probable conclusion is that the building was originally not a church but a library, and that it was transformed into a church at some subsequent period in its history to meet some special demand. [Illustration: PLATE LXXIX. GASTRIA (SANJAKAR). FROM THE WEST.] [Illustration: GASTRIA (SANJAKAR). THE INTERIOR. _To face page 270._] [464] P. 304. [465] Banduri, iii. p. 54. [466] Leo Gram. p. 214. [467] Zonaras, iii. p. 358. [468] Theoph. Cont. pp. 625, 628, 790. [469] _Ibid._ p. 90. [470] Theoph. Cont. pp. 91-92. [471] _Ibid._ pp. 174, 658, 823; Codinus, p. 208. The Anonymus (Banduri, iii. p. 52) and Codinus (_De aed._ p. 97) say that Theodora and her daughters were confined in the convent of Euphrosyne at the Libadia, [Greek: ta Libadia]. Their mistake is due to the fact that the convent at Gastria and the convent at Libadia were both connected with ladies named Euphrosyne. Cf. Codinus, p. 207. [472] Constant. Porphyr. p. 647. CHAPTER XXI THE CHURCH OF S. MARY OF THE MONGOLS