Roughly forty underground cities have been located in the Cappadocia region, and today six are open to visitors. Many were initially begun during the Bronze Age and completed by the seventh century BCE, serving as protection during increasing perods of invasion and external threat. Stout rolling-stone doors prevented invaders from entering. Deep wells provided water. Wine presses, oil storage, livestock pens, kitchens, and elaborate churches were carved out of the rock so that the inhabitants could live for months underground, until it was safe to emerge and return to their ground-level villages.
The largest and most elaborately excavated underground cities are at Kaymaklı and Derinkuyu. Scholars believe that many early Christians escaping persecution by the Roman Empire took refuge at Derinkuyu. Extending more than sixty meters underground, the city could be closed from the inside with large stone doors, and each floor could be sealed off separately, providing shelter for up to 20,000 people. Unique to the Derinkuyu complex and located on the second floor is a spacious room with a barrel-vaulted ceiling, perhaps used as a religious school. Distinct in structure and layout from Derinkuyu is Kaymaklı, known in ancient times as Enegup. The houses in the modern-day village above are constructed around the nearly one hundred tunnels of the underground city, and the tunnels are still used today as