Hierapolis Plutonium (Pluto's Gate)

Strabo describes the Plutonium at Hierapolis in Book 13 of his Geography. In H. L. Jones's translation, it is "an opening of only moderate size, large enough to admit a man," enclosed by a quadrilateral handrail, and the space inside is "full of a vapour so misty and dense that one can scarcely see the ground." The air outside the rail is harmless in calm weather, but "any animal that passes inside meets instant death." Bulls led in "fall and are dragged out dead." Strabo adds, "I threw in sparrows and they immediately breathed their last and fell."

The exception was the Galli, the eunuch priests of Cybele. Strabo writes that they "pass inside with such impunity that they even approach the opening, bend over it, and descend into it to a certain depth, though they hold their breath as much as they can." He saw "an indication of a kind of suffocating attack" in their faces. He offers four explanations: all eunuchs are immune, or only those around the temple, or it is divine providence, or the priests have "certain physical powers that are antidotes against the vapour."

Pliny and Cassius Dio

Pliny the Elder says that at Hierapolis "no one can enter with safety, except the priest of the great Mother of the Gods." Cassius Dio, who says he tested the opening with birds and bent over it himself, writes that "a theatre had been built over it" and that it kills everything except "human beings that have been emasculated." He adds, "The reason for this I cannot understand."

The 2013 announcement

In 2013, Italian archaeologists led by Francesco D'Andria of the University of Salento announced at a conference in Istanbul that they had found the Plutonium. "We found the Plutonium by reconstructing the route of a thermal spring," D'Andria told Discovery News. The team reported the remains of a temple, a pool, and steps above the cave, and an inscription dedicating the place to Pluto and Kore, deities of the underworld. Archaeology magazine reported in November 2013 that it had also found two statues in the thermal springs, a three-headed Cerberus and a snake rolled onto itself, damaged "probably by Christian pilgrims" between the 4th and 6th centuries A.D.

The gas

A paper published in 2019 in Archaeological and Anthropological Sciences measured the gas. Hardy Pfanz and three co-authors found carbon dioxide "at deadly concentrations of up to 91%" in a grotto below the temple of Pluto, and 4 to 53 percent outside its mouth, depending on height above the ground. At night, they write, the gas reaches concentrations "that would easily kill even a human being within a minute." They trace it to the Babadağ fracture zone, an active seismic structure that crosses the old town. The paper's abstract does not mention the priests.

Coşkun Daşbacak, deputy to the excavation's director, Grazia Semeraro, told the Turkish newspaper Sözcü in 2021 that carbon dioxide is heavier than air and collects at ground level at night, and that it disperses quickly on hot, sunny days.

Since 2022

The area was closed after the 2013 excavation because of the gas. It opened to visitors on June 20, 2022, according to reports the next day from the news agencies DHA and İHA. A walkway built at a distance the gas does not reach runs around the structure, and statues of Hades and Cerberus, which the Denizli Museum's director said in 2018 were made to match the originals, stand on a terrace beside the gate. The area beyond the gate is closed to visitors.

The gate is viewed from the walkway, and visitors do not go beyond it. It stands inside the Hierapolis archaeological site, which has a South Gate, a North Gate, and a pedestrian entrance. On October 15, 2026, the Ministry of Culture and Tourism's page for the site listed hours of 8am to 6pm every day, with the ticket office and pedestrian entrance closing at 5pm. The page gave no price.