But more interesting than either of these is that unique building which the Turks have happily named "Kutchuk Aya Sofia," little S. Sophia, the Church of S. Sergius and S. Bacchus.[53] It stands not far from Koum Kapoussi in the Marmora Walls, and quite close to the railway. Originally it was connected with the Church of S. Peter and S. Paul. Procopius describes the churches as standing obliquely towards each other, "joined together, and vieing one with another. They have," he says, "a common entrance, are equal to one another in all respects, are surrounded by a boundary wall, and neither of them exceeds the other or falls short of it, either in beauty, size, or any other respect; for each alike reflects the rays of the sun from its polished marble, and is alike covered with rich gold and adorned with offerings. In one respect alone they differ, that the one is built longitudinally, whereas the columns of the other for the most part stand in a semi-circle. The portico at their entrance is common to both, and from its great length is called narthex (_i.e._ a reed). The whole propylea, the atrium, and the doors from the atrium, and the entrance to the palace, are common to both." A door now closed at the south of the narthex shows where was the entrance to the Church of S. Peter and S. Paul. S. Sergius and S. Bacchus has happily suffered but little. It has, as has been said, a structural narthex. The atrium can still be traced in the arrangement of the Turkish houses and garden separated now from the church by a narrow pathway.
The Church of S. Sergius and S. Bacchus is a square with a dome. Columned exedras fill out the angles of the square under the domed vaults, and the piers supporting the dome form an octagon. A small apse is added at the east end. The ground plan of the church almost exactly repeats that of S. Vitale at Ravenna, which was probably begun a year before its companion in Constantinople. The resemblance is most marked in the six windows of the apse, the galleries and the columns on which they rest. The details also of the work closely resemble each other. We have the simplest form of the impost capital and the eight-lobed melon-formed capital. Vine-leaves form part of the decoration of some of the capitals and of the frieze: some say that this is a fanciful allusion to the associations of the name of one of the saints to whom the church is dedicated. Many crosses are cut in the marble of the west gallery; and on the south side over the imperial entrance from the palace are the monograms of Justinian and Theodora.