Cisterns are installations for the storage of water and can either be underground or open reservoirs above the ground. Open cisterns (such as those of Aetius and Aspar) can be found in the belt between the Constantinian and Theodosian walls, since the land was devoted to agriculture. Water from open cisterns was therefore likely destined for supplying public fountains, industrial and agricultural purposes. Water for consumption was more likely stored underground.
Cisterns above the ground dealt with water pressure issues. Therefore, many ground-level cisterns were reinforced at the corners, which were typically angled or curved. Later cisterns also made use of convex ('curved' walls) reinforcement (Crow et al., 2008, p. 137).
Citizens were obliged to collect their water from designated reservoirs; diverting water from the aqueduct itself was severely punished (see Cod. Theod. 6.4.29).
By the Palaeologan period, many cisterns had lost their names (Crow et al., 2008, p. 22).
In the early period, water pressure of these open reservoirs was presumably controlled by sluice-gates. Crow et al., 2008, p. 131 note that the smaller closed ‘satellite’ cisterns (C3/2, D4/1 near the Aetius and Aspar reservoirs) may have been involved in regulating the flow from the reservoirs.
Open cisterns fell out of use in the Middle and Late Byzantine Period due to the destruction of 1204 and lack of maintenance (Altuğ, 2013, p. 120).