“The thermal waters are likely one of the primary reasons for the city’s foundation,” said Dr Sarah Yeomans, an archaeologist at the University of Southern California who specialises in the Roman Empire. “By the mid-2nd Century, Hierapolis would have been a beautiful, bustling spa-town with what I imagine was a more dynamic and diverse population than most, given the popularity of such places with visitors.”
But Hierapolis was also known throughout the Roman world for another, more sinister reason. It was said to be the location of a “Gate to Hell”, a portal to the underworld where the toxic breath of the three-headed hellhound Cerberus flowed out of the ground, claiming unsuspecting victims on behalf of his master, the god Pluto. A shrine – the Ploutonion – was built on the site, and pilgrims travelled from across the region to pay the priests of the temple to make sacrifices to Pluto on their behalf.
Writers of the time, including Pliny the Elder and the Greek geographer Strabo, described these sacrifices as a chilling spectacle. A priest would lead an animal, perhaps a sheep or a bull, into the shrine. As if by the hand of the god, the animal would instantly drop dead, while the priest would walk out alive. “I threw in sparrows, and they immediately breathed their last and fell,” wrote Strabo in Book 13 of his encyclopaedia Geography, clearly astonished by what he had just witnessed.
When you visit the Ploutonion today it’s hard to imagine these dramatic scenes being real. Now excavated and restored, it’s a tranquil place: a rectangular enclosure filled with about 25cm of sparkling clear water topped with gently drifting mineral foam, and a small arched entrance on one side. Above it is stepped seating for spectators, and a replica statue of Pluto gazes benignly down into the arena. When I visited, I couldn’t understand how this could be a place of death? Surely these are made-up stories, I thought. How could the priests survive while the animals die?
These were questions that also intrigued Hardy Pfanz, a volcano biologist from Germany’s University of Duisburg-Essen who studies geogenic gases – gases given off during geological processes. “When I read the descriptions from the ancient writers, I began wondering if there could be a scientific explanation,” he said. “I wondered, could this Gate to Hell be a volcanic vent?”