Through a basement door in southeastern Turkey lies a sprawling underground city -- perhaps the country's largest -- which one historian believes dates back to the ninth century before Jesus Christ. Archaeologists stumbled upon the city-under-a-city "almost by chance" after an excavation of house cellars in Midyat, near the Syrian border, led to the discovery of a vast labyrinth of caves in 2020. "In order to protect themselves from climate conditions, enemies, predators or contagious diseases, people sought refuge in these caves -- and they later became an underground city," explains art historian Mervan Yavuz. IMAGES AND SOUNDBITES ARRANGED IN SEQUENCES