Derinkuyu: (Underground City)
Wikipedia says of it: 'First built by the Phrygians in the 8th-7th centuries B.C according to the Turkish Department of Culture, the underground city at Derinkuyu was enlarged in the Byzantine era. The oldest written source about underground cities is the writings of Xenophon (ca. 431 – 355 BC). In his Anabasis 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, they were believed to have 'been constructed at around 1,400 BC by the Hittites'. - Chop Suey
A Hittite connection is confirmed by archaeology, but the exact date remains elusive:
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. 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. - Rough Guides
3) Tracy T. Twyman, Richard Metzger. The Arcadian Mystique. 2005. Dragon Key Press.
Originally posted on: Ancient Wisdom