Known today as the ‘Little Saint Sophia Mosque’ ( Küçük Aya Sofya Camii), the Byzantine church of Saint Sergius and Bacchus dates to the beginning of Justinian’s reign in 527 AD. Popular belief attributes it to the same authors of Hagia Sophia, Anthemius of Tralles and Isidorus of Miletus, but there are no proofs of such authorship. However, it is commonly accepted that the project was well known in the Western part of the Empire, and served as model for the church of San Vitale in Ravenna. Huseyin Aga, head of the Eunuchs of the Sultan’s Palace, transformed the building in a mosque between 1506 and 1513. One of the most peculiar features of Saint Sergius and Bacchus is undoubtedly the ‘pumpkin-shaped’ dome which embraces the space of prayer.