The God of Hidden Waters…
is not only in the novel Trunk of Scrolls, he is the God who provides for you before you even ask or imagine.
The place Justin, Marcellus and Byziana found in Justinian’s Constantinople was indeed an ancient and hidden water reservoir rediscovered during the time of Justinian.
This cistern was featured significantly in the new Tom Hanks movie Inferno
For more information on the Basilica Cistern (the Underground Cistern)… take a look at these sites:
YEREBATAN SARNICI: The Official Site for the Underground Cistern
CITIES OF THE UNDERWORLD SERIES: ISTANBUL (study guide)