Geological explanation of Roman gate to underworld

A study identifies the reason why the ancient Romans believed that the gate to the underworld was located at the city of Hierapolis, modern-day Turkey. The cave entrance emits volcanic carbon dioxide which even today kill birds that fly to close.

Digital reconstruction of Plutonium at Hierapolis – gate visible below the stone seating (by Massimo Limoncelli)

The city is located in region’s most geologically active areas. The Romans believed that the thermal springs located there had healing powers. The gate known as the Plutonium, for Pluto, the god of the underworld, is located over a deep fissure running beneath the city, emitting carbon dioxide. The vapour forms as a visible mist. Team under volcano biologist Hardy Pfanz from the University of Duisburg-Essen has measured the CO2 concentration in the arena over time, revealing that during the day, the sun’s warmth dissipates the gas, but at night the gas, being slightly heavier than air, forms a CO2 “lake” on the sheltered arena floor. At dawn the CO2 concentration 40 centimetres above the arena floor reaches 35%, enough to asphyxiate and kill animals or even people within a few minutes. It is believed that similar research might help to identify the exact location of an ancient gate to hell at a site called Akaraka, also in modern-day Turkey.

(after Science & Massimo Limoncelli)

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