Mysterious ‘portal to the underworld’ in Turkey

The ancient city of Hierapolis has long hidden a poisonous secret in its mysterious “Gate to Hell”. But modern science has finally uncovered the truth behind the Roman myths.

Two millennia ago, a small Greco-Roman temple in present-day Turkey awed and enthralled its residents. Just beyond its stone gate, in a grotto shrouded in a heavy mist, a strange force worked dark deeds: Bulls ushered inside would lie down and perish; the castrated priests in charge would emerge unscathed.

Was it the bloodthirsty will of Pluto, the god of the underworld? The supernatural power of the priests? New research published on Feb. 12 in the journal Archaeological and Anthropological Sciences suggests a far earthlier explanation to the cave’s mystery: noxious carbon dioxide.


(The noxious gas is heavier than oxygen, so it settles lower, which is one reason CO₂ leaks in your house make basements deadly.) Animals with noses to the ground likely breathed in far more gas than the humans walking upright beside them, which could explain the priests’ miraculous imperviousness.

Although rediscovered only in 2013 near the town of Pamukkale — famous for its surreal, Unesco-designate travertine hot spring terraces — the cave’s existence has been known since antiquity as part of what was then Hierapolis. Known as “Plutonium” after Pluto, it was thought to be a gate to the underworld and a way to convene with the god by offering animal sacrifices. Spectators would watch in disbelief from a nearby arena. A description written by the Greek geographer Strabo, who lived from 63 B.C. to 24 A.D., makes a great deal more sense given what we know today: “This space is full of a vapor so misty and dense that one can scarcely see the ground … bulls that are led into it fall and are dragged out dead,” he wrote. But althoug

h priests entered and left the cave unharmed, Strabo noted that they would “hold their breath as much as they [could]” and displayed “an indication of a kind of suffocating attack.”

By Bella Falk
29th June 2021

The silver lining? Fear generally keeps tourist crowds at bay. Should you visit, you might have the plutonium all to yourself.


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