After more than 2,000 years, the mystery of the hell gate was opened

Once a ancient tourist destination, the Plutonium cave, also known by its Vietnamese name, "contains a secret that must be explained by modern scientists after 2,000 years."

Two thousand years ago, the ancient tourists went to a Greek-Roman temple in Hierapolis (modern-day Turkey), located above a cave that was supposed to be the gate to the afterlife. Their purpose is simple: watching animals, from birds to cows, collapsing in front of the cave. This cave called 'Plutonium' - placed under the god of hell Pluto in Greek mythology - is believed to be able to spew out the "death breath" , depriving the lives of any creature daring to approach, except for senior priests. They are people with immunity to 'death breathing' and have the task of bringing animals into the cave to sacrifice.

Pliny ' Elder ' natural historian described this phenomenon as 'the tribute of Charon' - a boatman who takes dead souls across the Styx River and the Acheron River to return to the hell realm in Greek mythology.

Toxic gas

Road to Plutonium cave.

However, today, scientists have lifted the mythical curtain behind this supernatural phenomenon. According to a study published in Archeology and Anthropology last February, a crack in the surface of the earth, located deep in the cave, produced CO ₂ with a concentration of 'death '. Specifically, with a portable gas analyzer, Mr. Hardy Pfanz and a group of volcanic researchers found CO2 with a concentration of 4-53% at the mouth of the cave and highest at 91% inside. This concentration is more than enough to kill all living things.

'The types of mammals (including humans) may begin to encounter problems below 5% CO2,' Pfanz told CNN. 'At 7%, the longer you stay, the more severe symptoms are sweating, dizziness, and heart rate. Higher concentrations lead to suffocation due to lack of oxygen as well as blood, acidified brain cells . '.

Therefore, all animals entering the cave quickly collapsed. Pfanz revealed that, during the study, the team found the bodies of several birds, mice and more than 70 beetles.

Tourist attraction

Like in the past, today, Plutonium still attracts thousands of tourists every year. Italian archaeologist Franceso D'Andria, who rediscovered the cave in 2013, said he and his colleagues also found evidence of a stand that had been built around Plutonium to serve Ancient tourists.

The ancient Greek geographer Strabo once described: 'Any animal that comes in will face instant death. The bulls that were led inside were collapsed and pulled to the outside. I threw a few sparrows and they immediately fell down , ' he wrote.

Graphics simulate buildings around Plutonium, including seats for the audience.

Strabo realized that this reaction was related to gas - the space was so full of smoke that it could not see the ground clearly " - but did not understand why gas affected animals but the monks unharmed. He said that they might be protected by the gods or simply the monks who had stopped breathing when entering the cave.

However, Mr. Pfanz's research also outlined the mystery behind this: monks and animals have different heights! It is known that CO _{2 is} heavier than oxygen, so it sinks down, forming a toxic 'gas lake' on the ground. Therefore, the animals will "receive enough" and the priests are safe.

'The nose of the animals is right at the level of the poison gas lake , ' Mr. Pfanz said.

In addition, Pfanz said that monks are aware of the origin of the 'death breath' as well as the change in gas concentrations from time to time during the day. The results also indicate that CO2 levels are quite high at sunrise and sunset because of the scattered sunlight. However, D'Andria, an archaeologist, disagrees with this view. He said that, based on finding many oil lamps at the entrance of the cave, 'it is very likely that many religious activities are carried out at night'.