Interpreting the subterranean building (the Crypt) in the northern courtyard of Hagia Sophia in Constantinople

The paper discusses a subterranean building situated north of Hagia Sophia in Constantinople, which was the object of a recent survey. Although it is generally accepted that the edifice has more than one phases of use, the date of its construction and its original use is problematic since the building is not mentioned in any written source and until recently has been the object of few surveys. The aim of this paper is to present the underground building in detail giving all new data, to establish a possible date for its construction and discern the different phases of use considering the available written sources about the adjacent church of Hagia Sophia as well as the remains and the archaeological data of the previous surveys.