The Fildamı Reservoir is an open basin measuring 127 × 76 × 10 meters (approximately 9,600 m²), reinforced against a hillside on its west wall. A later-built tower with a cylindrical chamber was added to regulate water pressure, as the reservoir originally featured multiple outlets at varying heights to manage the force of the water. Staircases on the north and south walls, supported by blind arches, likely provided access to these sluice-gates.
The reservoir’s water supply remains uncertain—possibly from local springs or a branch of the Valens Waterway (Thrace-line). Some of its water may have been channeled to the nearby imperial palace at Hebdomon. Primarily, the reservoir served troops and animals gathering on the adjacent kampos before and after military campaigns.
Surveyed by Crow et al. in the early 2000s, the site now hosts an athletics track in Bakırköy (ancient Hebdomon).
