[2] The building was erected on the top of the sixth hill of Constantinople, on a plateau which is limited by the open air Cistern of Aetius (now a football field) and by the unidentified Byzantine edifice denominated in Ottoman times as Boĝdan Saray.

Despite that in 1506, under the reign of Sultan Bayezid II, a pious foundation endowed by Kasım Bey bin Abdullah (possibly at that time Sekbanbaşı, that is, chief (Turkish: Agha) of the Janissaries), had a small mosque erected on the ruins of the building.

[1] The small mosque was heavily damaged by the 1894 Istanbul earthquake[4] and by the Salmatomruk fire on 2 July 1919, so that afterwards only the perimeter walls and the base of the minaret were still standing.

The Byzantine edifice was also roughly square in plan, with a single nave preceded by an atrium at NE and a projecting room on the east side.

The analysis of the brickwork during the restoration showed different construction phases,[1] and revealed that the foundations and the surviving walls were made of brick and stone.