The Plutonion (plutonium) at Hierapolis, "Place of Pluto was a religious site dedicated to the god Pluto (the classical Greek god of the underworld, Hades), in the ancient city of Hierapolis near Pamukkale in Turkey's. The site was discovered in 1965 by Italian archaeologists, who published reports on their excavations throughout the decade. The site is built on top of a cave which emits toxic gases such as carbon dioxide, hence its use as a ritual passage to the underworld. Ritual animal sacrifices were common at the site. Animals would be thrown into the cave and pulled back out with ropes that had been tied to them. Archaeologists noted that the fumes emitted from the cavern still maintain their deadly properties as they recorded passing birds, attracted by the warm air, suffocated after breathing the toxic fumes. For safety the original opening has been bricked up.