An archaeological dig in Turkey has uncovered what researchers believe is the largest subterranean city in the world.

A cave was discovered in the Midyat district in the southeastern province of Mardin that revealed passageways leading to a complex comprising water wells, silos, and places of worship–all dating from the 2nd and 3rd centuries, according to a report by Turkish newspaper, the Daily Sabah.

“Midyat has been used uninterruptedly for 1,900 years,” Gani Tarkan, director of the Mardin Museum, who led the excavations, told the Daily Sabah. “It was first built as a hiding place or escape area. As it is known, Christianity was not an official religion in the second century.”

He added that families who accepted Christianity were known to take refuge in underground cities to escape persecution by authorities. “Possibly, the underground city of Midyat was one of the living spaces built for this purpose,” he added.

Similar underground cities have been unearthed across Turkey. Cappadocia, in eastern Anatolia, what is now central Turkey, contains some 200 ancient settlements carved out of the region’s soft volcanic rock during the 7th and 8th centuries. Historians believe these caves originally provided the region’s inhabitants refuge from foreign invaders, and in the 14th century were utilized as hideouts by the Christian minorities from the occupying Ottoman forces. The cities were not fully abandoned until 1923, after the end of the Greco-Turkish wars. They were rediscovered in 1963, supposedly when a man found a hidden room behind his walls.

The most famous underground city in Cappadocia is the multilevel complex Derinkuyu, built sometime between 780 and 1180, some 200 feet belowground. It had the capacity to shelter around 20,000 people in addition to livestock. Wine cellars, stables, chapels, and a religious school were uncovered amid passageways that linked Derinkuyu to other such settlements.

The newly unearthed Midyat city, however, dwarfs Derinkuyu in comparison. It could hold “at least 60–70,000 people,” according to Tarkan.