According to the Turkish Department of Culture, Derinkuyu was first built by the Phrygians in the 8th-7th centuries BC, and then was enlarged in the Byzantine era. The oldest written source about those underground cities is the 'Anabasis' by Xenophon.
He writes that the people living in Anatolia had excavated their houses underground, living well in accommodations large enough for the family, domestic animals, and supplies of stored food.
Alternatively, the underground cities in Turkey were believed to have been constructed at around 1,400 BC by the Hittites. This could be confirmed by archaeological finds, but the exact date remains unknown.
The Tribe from the Depths of the Earth
In origin, the cities are thought to date back to Hittite times at least 1900-1200 BC. Hittite-style seals have been found during excavations and other Hittite remains, such as a lion statue, have turned up in the area.
It is possible that the underground rooms were used as shelters during the attacks of 1.200 BC, when the Hittite Empire was destroyed by invaders from Thrace.
The Hand Carved Longyou Caves Mystery
Later the complexes were enlarged by other civilizations, and the presence of missionary schools, churches and wine cellars would seem to indicate that they were used by Christian communities.
No matter who and when built those underground cities, they are considered one of the best examples of ancient engineering thought.