In the ancient city of Hierapolis, Roman priests led sacrificial bulls down a path and through an eerie stone gate that opened to a cave-like grotto filled with a thick, gloomy mist. In that grotto, the bulls mysteriously dropped dead, but the priests emerged unscathed. Some people began to believe the gate, and others like it across the Mediterranean region, were actually the portals to hell as described in Greek and Roman mythology. Now researchers from the University of Duisburg-Essen in Germany believe they discovered a scientific explanation for the phenomenon, Science reported.
The stone doorway, rediscovered seven years ago in modern-day Turkey, stands in one of the area’s most geologically active regions. Even today a deep fissure beneath the site constantly emits a visible mist of volcanic carbon dioxide. The gate, known as the Plutonium, for Pluto, the mythical god of the underworld, sits directly above it and still often claims the lives of birds that venture too close.
The researchers discovered that daytime temperatures dissipate the carbon dioxide, but at night a deadly gas lake collects on the arena floor. By dawn, the carbon dioxide concentration at a height of 15 inches above the floor reaches 35 percent, a saturation level high enough to asphyxiate animals and people within minutes. But concentrations fall rapidly at greater heights.
Hardy Pfanz, a volcano biologist and one of the researchers, told Science the priests likely performed their sacrifices only in the morning or evening hours when the carbon dioxide levels reached their highest point. The bulls lacked the height to keep their heads fully above the noxious gas, and as they became dizzy their heads likely fell lower, exposing them to even more deadly concentrations. But the priests stood tall enough to breathe safely. —J.B