Open reservoir of 127 × 76 × 10 m (=c. 9,600 m2) buttressed against the hillside (west wall), including a later built tower with internal cylindrical chamber (for reducing the pressure of water exiting the reservoir) (Crow et al., 2008, p. 127, 131). Before the tower was built, the reservoir appears to have had outlets at various heights in the external walls that could be opened. The water pressure would have been too high for a single outlet at the bottom. Both on the north and south side a pair of staircases was built against the wall; supported by an arcade of five blind arches. These staircases may have been used to access the sluice-gates at various heights.
It is not exactly clear how this cistern was supplied. It could have been the springs higher up in the valley, or a channel, branching from the Thrace-line (Valens Waterway). Some of this reservoir's water may have been piped to the nearby imperial palace at the Hebdomon; a channel was reported leading south of the structure (Crow et al., 2008, p. 134).
It most likely served the troops and animals that mustered before and after campaigns on the nearby kampos (Crow et al. 2008, p. 134).
During the early 2000s, Crow et al., 2008 were able to conduct a survey at Fildamı (p. 7).
Today, the Fildamı cistern houses an athletics track in Bakırköy (ancient Hebdomon).
