The structure at the end of Small Hagia Sophia Street and used today as a mosque was a church made between 531 and 536 by Byzantine Emperor Justinian I.
Small Hagia Sophia that served as a for nearly a thousand years was turned into a mosque by Babüs Saade Ağası (the chief of the Aghas) Hüseyin Agha in 1506 during the time of Beyazid II. On the west side of the structure, a last congregetion arcade suitable with Ottoman architecture, madrasah rooms to the surrounding of the small courtyard and a hammam was added on the side street.
The place of worship was of 25×28 meters in a rough square shape. Except for the mihrab bulge, there is a gallery floor that surrounds the whole structure in octago shape. Since pendantives are not used in the dome that covers the main location, adopting this octagon brought forth the vawed dome structure. The dome is 19 meters high and its diameter exceeds 15 meters.
On the gallery floor, on the epigraph surrounding the structure, it is said that Justinian I had the church built in the name of Saints Sergius and bacchus. Monograms of Justinian I and his wife Theodora can be seen on the column headings on both floors.
Address: (Saint Sergius and Saint Bacchus Church), (Küçük Ayasofya Camii) Küçük Ayasofya Avenue.