The Cistern of Modestus is likely the first attested cistern in the sources. Placed in Region XI (Notitia), probably close to the Church of the Holy Apostles (present day Fatih Camii complex); its altitude suggests it was supplied by the Valens Waterway (Crow et al., 2008, p. 13). Janin, 1964, p. 209-210 categorises it as a covered cistern; Altuğ, 2013, p. 46-47 identifies it as an open cistern with no surviving remains in the present day.
Literary evidence
According to the Patria, Modestus was one of the eight patricians brought from Rome by Constantine, who built his house near the Holy Apostles, including a cistern close to his house (Region XI). A Cistern Modestiaca is indeed attested there in the Notitia (early 5th century) (Janin, 1964, p. 209).
According to Crow et al., 2008 , p. 15, the Cistern of Modestus could also be the cistern listed as "Of the Archangel" in Codex Matritensis Graecus.
When Gilles describes Constantinople in the mid-16th century, he remarks that the cistern of Modestus was gone: "Mohamet, the same emperor, built in this place [around Fatih comples] the largest baths in all the city (Çukur Hamamı, at the east corner of teh Fatih Camii complex) where the old cisterns of Arcadius or Modestus had formerly been." (Gilles, De Topographica Constantinopoleos 3.9, trans. Ball and Musto (1988), 165).
Archaeological evidence
Possibly to be identified with the cistern (D5/4, c. 154 m ×90 m, surface area 14,000 m2) between the Bozdoğan Kemeri and Sehzadebaşı Caddesi (noted by Gilles, 16th century) in the Saraçhane. However, there are also other cisterns mentioned near this location, such as the Arcadiaca, the latter which has not been identified (Crow et al., 2008, p. 127-128).
Altuğ, 2013, p. 31 comments on Gilles' observation that the ruins in Saraçhane/Çukur Hamamı (analysed by Forchheimer and Strzygowski (1893) do not exist anymore in the present day.