The truth about the infamous "Gate to Hell" has been uncovered — and it's no less fascinating than the myth.
A research team from University of Duisburg-Essen in Germany recently discovered that the fables about human and animal sacrifices at this ancient Roman site are, in fact, true.
The "Gate to Hell" — discovered near the modern-day city of Pamukkale in Turkey — is the fabled Plutonium, a site where oracles and priests would perform sacrifices to Pluto in the ancient city of Hierapolis. Plutonium is named after Pluto, Roman god of the underworld.
The area where the gate would have been centuries ago has significant levels of carbon dioxide (roughly 35 percent) emanating from the ground — especially at night and in the early morning. The gas dissipates during the day.
However, the carbon dioxide only reaches lethal amounts 40 centimeters from the ground, which would explain why priests would sacrifice animals there — and sometimes even people — but not die themselves.
"They … knew that the deadly breath of [the mythical hellhound] Kerberos only reached a certain maximum height," biologist Hardy Pfanz told Science Magazine.
A deep, narrow opening in the ground emits the carbon dioxide in the form of a mist, right below where Pluto's Gate was constructed and even still today.
Pluto's Gate was discovered in 2011 by a team led by Francesco D'Andria, a professor of classic archaeology at the University of Salento in Italy. The researchers were following historic texts that put the location of Plato's Gate in the ancient city of Hierapolis, which was built near the therapeutic hot springs in southwest Turkey beginning in the third century B.C. in an area that would later become Pamukkale.
According to ancient texts, the gate — or "Pamukkale" in Turkish — contained deadly vapors that would kill any animal that entered the cave, yet certain priests could withstand the fumes. "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."
The site was mostly destroyed by earthquakes in the sixth century, but D'Andria says the research team found evidence of the temple that was originally built outside the cave, where Greco-Roman pillars and steps once led down into the toxic entrance to Pamukkale itself. "People could watch the sacred rites from these steps, but they could not get to the area near the opening," D'Andria told Discovery News. "Only the priests could stand in front of the portal."
Hierapolis-Pamukkale was declared a UNESCO World Heritage site in 1988. Millions of tourists visit the site each year to see the ruins of Greek baths, temples and monuments.
Editor's Note: This article has been updated since it was originally published in April 2013.