An underground cistern recorded by Marcellinus, located near the column of Constantine. The forum of Constantine was likely supplied by the Valens Waterway.

In 2008, when Crow et al. published their work, no excavations had been done at Constantine's forum (p. 128). For excavations, see Bayülgen and Saner, 2024, p. 275-277. There are multiple cisterns in proximity, identification must be done meticuously.