The Reservoir of Aetius is a massive open water reservoir measuring 244 × 85 meters, with walls 13–15 meters high and a capacity of 269,620–311,100 m³. Due to water pressure, it could only be safely filled to a depth of 9.5 meters. A 1.20 × 0.67 m channel in the northwest wall, located 6 meters above the floor, may have served as a later high-level outlet or maximum capacity marker.
Built alongside the new high-level water supply, its rectangular shape was dictated by the slope of the terrain. The structure features alternating bands of brick (0.35 m) and stone-faced mortared rubble (1.8 m), with the north wall measuring 5.2 meters thick.
Today, the former Reservoir of Aetius is used as a sports stadium.
