The First Hill of Byzantium, the Greek city’s Acropolis, was later the site of the Topkapı Sarayı. Within the 55ha enclosure of the Ottoman palace are the remains of the First and Second regions of the Byzantine city including the church of Hagia Eirene and the excavated traces of other churches and buildings, but commonest are the remains of at least 33 Byzantine cisterns. Based on previous documentation and more recent observations we aim to explore their topographical setting and establish how the hydraulic infrastructure evolved over more than a millennium. In particular we address the question of changing sources of water, from the external aqueducts to rainwater harvesting. Initially we present the setting and distribution of cisterns over three distinct areas: the east flanks of the First Hill down to the Sea Walls but excluding the Mangana, the level hill including the four courts of the Saray and the west slopes including Gülhane Park. The evidence then turns to a consideration of the Byzantine written sources and Ottoman accounts of the Acropolis and the Saray. Finally, there is an attempt to interpret the subsurface as a source for the urban topography of the Byzantine district, and to set the remains in the wider context of evolving water usage and technology transfer from the Byzantine to Ottoman city. Details of the individual cisterns and their location are to be found in the online Appendix together with illustrations.*