In 1963, a man renovating his home in Turkey discovered the ancient city of Derinkuyu after noticing his chickens kept disappearing through a crack in his basement. The hidden 18-level underground city extends 85 meters (279 feet) below the surface and could shelter up to 20,000 people. Derinkuyu, located in central Turkey, is the largest of more than 200 underground cities discovered in the Cappadocia region. Descending 18 levels beneath the surface, it featured an advanced ventilation system that supplied fresh air, along with deep wells that provided water for its inhabitants. The city also contained stables, storage rooms, chapels, guest quarters, and even a winery. Although its origins remain debated, most scholars believe Derinkuyu was first carved into the region’s soft volcanic rock by the Phrygians, an Indo-European people. As Phrygian influence declined under Roman rule and their language gradually disappeared, the underground city was later occupied by Greek Christians seeking refuge from war and religious persecution. By the Byzantine period, Derinkuyu had reached its greatest extent and served as a sanctuary during the Arab-Byzantine wars between the 7th and 11th centuries. It was also used as a refuge during the Mongol invasions in the 14th century. After the region came under Ottoman control, local Christians continued to shelter there during periods of unrest. The city was ultimately abandoned in 1923, when its Christian population was expelled from Turkey and resettled in Greece as part of the compulsory population exchange.(Historic Vids)