This historic site in modern-day Turkey may seem like a simple tourist attraction, but its reputation is far more sinister. Known as the ‘gate to hell’, the site is infamous for a string of unexplained deaths of cattle and other animals, leading many to speculate that it is home to a portal to the underworld. However, the mystery behind these grisly deaths may finally be solved (Photo: Getty Images) Situated in the Buyuk Menderes Valley, near Pamukkale and Denzilli, the ancient Roman site probably dates back to the second century. It became famous as a spa resort for its hot springs, located in the classical kingdom of Phrygia, near southwestern Anatolia. The springs were believed to have healing properties, and many people apparently retreated here to retire – a huge adjacent necropolis, replete with tombs, confirms this (Photo: Getty Images) But that's not the only thing it's famous for. The site features a stone doorway leading into a cave-like grotto built into the wall of the amphitheatre. It was long considered dangerous due to descriptions by the ancient Greek geographer and philosopher Strabo, who is believed to have visited the site around 2,000 years ago. His account of the grotto led many to believe it was an entrance to the underworld, as animals died “instantly” as they entered (Photo: Getty Images) In his book Geography, Strabo wrote: “It is a medium-sized opening, wide enough to admit a man, but it goes down to a considerable depth, and the space is full of vapours, so misty and thick that one can hardly see the ground. Oxen that are brought there fall down, and are carried out dead. I have thrown sparrows in, and they have died and fallen down straightway.” (Photo: Getty Images) The cave, named after the god of the underworld Pluto, was used by the ancient Romans for animal sacrifices, with castrated priests bringing livestock through the doorway as an offering to the gods of the underworld, then emerging unharmed while the creatures suffered from suffocation. Witnesses to these macabre rituals also paid money to purchase small animals such as birds and threw them into the cave, believing that the ‘breath of Hades’ was the cause of their demise. At the time, it was believed that the priests survived the grotto due to their castration (Photo: Getty Images) However, more recent research into the site has revealed what exactly was killing so many animals. In 2018, researchers discovered that the gate sits above a crack in the ground that is still releasing significant amounts of volcanic carbon dioxide (CO2). This forms a “lake” of the poisonous gas that rises 40 centimetres into the air. Although the levels were controlled during the day, when the gas was dispersed by the sun’s rays, they rose at night and peaked at dawn, when the lower levels of the cave were filled with gas (Photo: Getty Images) Research team leader Hardy Pfanz, writing on Science.org, suggested that the sacrifices occurred when CO2 levels were highest, and that the priests survived because they were tall enough
