Constantinople, now known as Istanbul, had a shortage of freshwater sources. To supply water to its growing population, a large number of cisterns were built in Late Antiquity. The city relied on its Thracian hinterland for water, as it had no rivers and few small springs. More than 200 cisterns from the Byzantine era have been documented in the city. The cisterns were essential for the city’s water supply and security during sieges. The largest and most famous underground cistern is the Basilica Cistern, built during the reign of Justinian I. Several large open-air water reservoirs were also built. The cisterns were supplied by a gravity-based system that brought water from the city's hinterland.
The recent examination of the city's cisterns has uncovered 160 of them, but it's believed that this only represents a small fraction of the original number. These cisterns were constructed over the lifespan of the Byzantine city and continued to be built during the Ottoman era. Some cisterns served as large public reservoirs for storage and distribution, while others were likely used for private purposes. It's not entirely clear whether the smaller cisterns were part of a larger water supply network or if they were solely for collecting rainwater from the roofs of churches and other buildings. Cisterns from the Roman period in urban areas are primarily found in North Africa and the eastern provinces. In Rome, the largest cisterns were reservoirs for the imperial bathhouses. The investment in the new city of Constantinople was much greater, partly due to the insecurity from barbarian peoples across the Danube. Other local factors, such as the karst limestone catchments for many water sources, led to uneven water flow throughout the year, necessitating storage at other times. This principle was first mentioned in Procopius' account of the construction of the Basilica Cistern by Justinian. Both the Basilica Cistern and the Binbirdirek were constructed in the sixth century. These structures faced similar challenges to modern underground car parks in densely packed cities and reflect the high cost of real estate in a crowded city in the sixth century. None of the structures from the fourth or early fifth century known from texts can be identified with certainty, but the pattern of cisterns with brick-vaulted roofs supported on columns, often with elaborate capitals, became the norm across the city. Observers have suggested that the forms of cisterns seen in Constantinople could be associated with and influenced by the extensive network of cisterns known from Alexandria. In Syria and Palestine, the pattern of cisterns followed the standard Roman form, even in late constructions such as the impressive cisterns from the Anastasian foundations at Dara (East Roman fortress city) and Resafa (a city, now in Syria). An analysis of the mortars and other building materials estimated that 2.5 million cubic meters of stone were needed to build the bridges and channels.