Derinkuyu Underground City

Derinkuyu is the deepest known of the underground cities of Cappadocia in central Turkey, rediscovered in 1963 when a resident knocking through a wall opened a passage into a vast tunnel network. The city descends about 85 m through roughly 18 carved levels and could shelter thousands of people, plausibly up to about 20,000 with food stores and animals. It includes stables, wine and oil presses, chapels, wells, ventilation shafts, and large circular stone doors that could be rolled to seal passages from the inside. Excavation likely began with the Phrygians around the 8th–7th centuries BCE and was greatly expanded in the Byzantine era, when Christians used it as a refuge.

Ancient Aliens and advocates of the ancient-astronaut hypothesis sometimes ask how ancient people could have engineered such a vast complex with deep ventilation, suggesting lost or otherworldly technology, or that the cities were dug to hide from cataclysm or from the ‘gods.’

The mainstream explanation is straightforward. Cappadocia’s tuff is exceptionally workable with simple iron and stone tools, the region is honeycombed with more than 200 such excavations because the geology invites it, and the engineering — vertical ventilation shafts, stepped levels, rolling stone doors — is well within the capabilities of Iron Age and Byzantine builders motivated by the very real need to hide from invaders. The complexity reflects centuries of incremental human labor.