Speak of noxious fumes and a modern researcher’s first thoughts fly to carbon dioxide. In The Daily Telegraph, we may read that “Archaeologists have uncovered ‘Pluto’s Gate’, an ancient gateway to Hell, in Turkey”:
A group of Italian archaeologists have announced they have found the legendary “Pluto’s Gate”, a portal filled with foul-smelling noxious fumes which inflicted a quick death on any person or beast that was driven into its embrace.
The temple complex in Hierapolis, now the volcanic-spring restort town of Pamukkale, featured in many ancient legends and historical texts.
“This space is full of a vapour so misty and dense that one can scarcely see the ground. Any animal that passes inside meets instant death,” the Greek historian Strabo wrote in 24AD*.
“I threw in sparrows† and they immediately breathed their last and fell.” [quoting Strabo’s Geographica, XIII, iv, 14]
Now, “foul-smelling noxious fumes” can’t be carbon dioxide because carbon dioxide is odourless. What were unspecified noxious vapours, however, are swiftly identified:
Francesco D’Andria of the University of Salento said the “visions” were probably hallucinations caused by breathing diluted fumes wafting up from the Gate to Hell.
And the portal is still a killer, he said.
“We could see the cave’s lethal properties during the excavation,” D’Andria told Discovery News.
“Several birds died as they tried to get close to the warm opening, instantly killed by the carbon dioxide fumes.”
* Strabo died, at the latest, around the year 24 when he was 87 or so; I doubt that he wrote the thirteenth of his seventeen books of Geographica in the last months of his long life.
† Strabo’s word, στρουθία, appears to refer to unspecified small birds rather than to sparrows in particular.