As the building consisted of an apse and a narthex in its initial construction, in later repairs and additions the main structure was kept intact; only an annex was made in the north of the structure, an outer narthex in the west, and a long and slender chapel was added in later years. This chapel is a long and slender building with a dome and is constructed over the cellar. The East end ends with an apse. All the round arches, semi-supports, niches in the outer fronts of the building, as well as the masonry and bricklaying workmanship contribute motion to the outer look of the building and save it from being a massive block.
The present building covers an area of 27.5 meters by 27 meters. The length of the Parecclesion is 29 m.The church has six domes, of which the greatist lies in the center with a diameter of 7.70 m. Two domes are located in the inner narthex, and the other two are situated at the right and left of the apse. The second .greatest dome after the central one, is located in the Parecclesion, with a diameter of 4.50 meters. The apse has three windows. The main building is covered with marbles of wonderful colours. The inner narthex is of 4 m. width and of 18 m. length. There is a door from here leading. to the Parecclesion. The outer narthex is of 4 m. width and 23.30 m. length. The niches in the outer narthex and in the annexed chapel have been used as tombs. The mosaics were made by drawing draft pictures on a fast drying plaster and sticking over them coloured pieces of stones, bricks and glass. As gold was also used in the mosaics during the . reign of Emperor Justinian, magnificient pieces of art had been created. In the XIV. Century during the Paiaiologos dynasty , the art of mosaic ornamentation has displayed a great development in Istanbul. The Chora Monastery built in this period is the most important evidence to this.
The themes dealt with in the inner and outer narthexes follow each other periodically just like the serial sequences of a comics book. On the northern wing of the inner narthex eighteen incidents describing the life story of the Virgin are depicted with all its beauty.
On the north of the outer narthex, important events in the lives of the holy family and the birth and baptizing of Christ are dealt with. The miracles of Jesus and his other deeds while diffusing the Words of God are dealt in the southern wings of both narthexes. But, because of the fall of the plasters, many of the important mosaics have not survived our epoch.
The short inscriptions seen on the mosaics are either symbols or writings explanatory to the mosaics. A harmonious blend of colours made in a natural way, creates a sense of admiration in those, who have the chance of looking at them.
We shall not follow the chronological order, but simply starting from the left of the enterance door, we shall see the wonderful mosaics in the outer narthex first, by following the numbers in our plan. Then, we shall conclude the tour of the museum, by visiting the inner narthex and the main section, and later on by visiting the annexed chapel.