The Open Reservoir of Aspar (Region XIV, Fifth Hill) measured 152 x 152 x 10–11 meters, with a surface area of 23,100 m² and a capacity of about 250,000 m³. Due to water pressure, it could only be safely filled to 7.5 meters. The structure alternated bands of brick (0.5 m) and stone-faced mortared rubble (1.2 m), with brick arches on the south-west wall.
Evidence suggests it was supplied by the Valens Waterway, though in- and output channels are no longer visible. Built alongside the new high-level water supply, its open design and location between the Constantinian and Theodosian walls imply agricultural use. Nearby closed cisterns may have helped regulate water flow.
Today, the site is a public park (the Çarşamba Çukurbostan Parkı) and children’s school.