A large Byzantine cistern (water tank) with five vaulted rooms divided by arcades is preserved intact under the square of Hagios Titos, between the church and the basement of a former industrial building (Mistiloglou Ice Factory). The tank was first discovered during the excavations for the construction of the Ice Factory and was recorded in 1965 in a document by Stergios Spanakis to the Municipality of Heraklion as an ancient temple that was converted into a tank.

Columns and capitals of the Roman and Early Byzantine periods have been reused in the arcades, as is the case in the cisterns of Constantinople. This fact, combined with its construction characteristics, suggests that the cistern was built in the Middle Byzantine period. In the Venetian period three single-room vaulted tanks were added north of the previous one and the complex was connected to the Morosini aqueduct.