Hierapolis is (Enc. Britt.) an “ancient Phrygian city in southwestern Turkey. … It was probably established by Eumenes II of Pergamum in 190 BC. It became a sacred city (hieron), its chief religious festival being the Letoia, named after the goddess Leto, a local variant of the Great Mother of the Gods, who was honoured with orgiastic rites. There was also a worship of Apollo Lairbenos. Hierapolis was rebuilt during the reign of the Roman emperor Tiberius in approximately AD 14–37 and survived until 1334, when it was abandoned after an earthquake. Extensive ruins, excavated since the 19th century, include baths, a gymnasium, an agora, and a Byzantine church.
This is the theatre, note the massive space under the stage.