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Deadly CO2 gases in the Plutonium of Hierapolis (Denizli, Turkey)


Using a portable gas analyzer system, the geogenic gas regime below and around an ancient gate to hell at Hierapolis/Phrygia was characterized. The site was first described by Strabo and Plinius as a gate to the underworld. During centuries, it attracted even ancient tourists. In a grotto below the temple of Pluto, CO2 was found to be at deadly concentrations of up to 91%. Astonishingly, these vapors are still emitted in concentrations that nowadays kill insects, birds, and mammals. The concentrations of CO2 escaping from the mouth of the grotto to the outside atmosphere are still in the range of 4–53% CO2 depending on the height above ground level. They reach concentrations during the night that would easily kill even a human being within a minute. These emissions are thought to reflect the Hadean breath and/or the breath of the hellhound Kerberos guarding the entrance to hell. The origin of the geogenic CO2 is the still active seismic structure that crosses the old town of ancient Hierapolis as part of the Babadag fracture zone. Our measurements confirm the presence of geogenic CO2 in concentrations that explain ancient stories of killed bulls, rams, and songbirds during religious ceremonies. They also strongly corroborate that at least in the case of Hierapolis, ancient writers like Strabo or Plinius described a mystic phenomenon very exactly without much exaggeration. Two thousand years ago, only supernatural forces could explain these phenomena from Hadean depths whereas nowadays, modern techniques hint to the well-known phenomenon of geogenic CO2 degassing having mantle components with relatively higher helium and radon concentrations.

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We want to thank the governorship of Denizli City for their kind help. We are indebted to Omer Faruk Gunay, vice governor of Eskisehir City, and Ismail Soykan, vice governor of Denizli City. The great help of the director of Hierapolis/Pamukkale is greatly acknowledged. The authors wish to extend their sincere thanks to the provincial culture and tourism directorate of Ankara and Denizli. Dr. Francesco Italiano kindly provided data about gas analysis from the grottos. Special thanks to Dr. Christiane Wittmann and Volker Wittmann for their excellent work in building a robust, continuously recording CO2 monitor. The authors are also grateful to Selami Yildirim and Mehmet Ergun from the Turkish State Meteorological Service. The authors are extremely thankful to Prof. Dr. Francesco D’Andria, who detected and excavated the new Plutonium at Hierapolis for his kind help providing a permission to work on the site, to his intelligent advices and to his permanent interest in the progress of our study.

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Correspondence to Hardy Pfanz.

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Pfanz, H., Yüce, G., Gulbay, A.H. et al. Deadly CO2 gases in the Plutonium of Hierapolis (Denizli, Turkey). Archaeol Anthropol Sci 11, 1359–1371 (2019).

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  • Carbon dioxide
  • Helium
  • Radon
  • Charonion
  • Gate to hell
  • Geogenic gases
  • Hades
  • Mephitic exhalations
  • Mofette