Pamukkale and Hierapolis developed around hot springs rising above the Lycus River valley in western Anatolia. Mineral-rich water flowed over the plateau edge, depositing white calcium carbonate that hardened into terraces, pools, and cascades resembling frozen cotton. The Attalid kings of Pergamon founded Hierapolis as a city and thermal center in the second century BCE, probably on an older sacred site. Its name may refer to Hiera, a figure in local tradition. Rome incorporated the region after the last Attalid king bequeathed his realm in 133 BCE.

Earthquakes repeatedly damaged the city, especially a severe event in the first century CE. Roman rebuilding created the monumental landscape now most visible: a colonnaded main street, gates, baths, fountains, temples, houses, theater, and one of Anatolia’s largest ancient cemeteries. Visitors sought the springs for bathing and healing, while residents used the abundant water for domestic and industrial purposes. The necropolis contains sarcophagi, tumuli, and family tombs belonging to people drawn from a wide region, evidence that the spa’s reputation extended beyond the city.

Hierapolis also possessed a sanctuary associated with the underworld. A cave released concentrated carbon dioxide from geological faults, killing animals close to the ground. Ancient writers described priests entering the dangerous space, which became known as the Plutonium. The same geology that produced sacred and therapeutic water could therefore appear both life-giving and lethal. The city’s theater, rebuilt in the Roman period, carried reliefs of Apollo, Artemis, Dionysus, and imperial ceremony, connecting local cult, entertainment, and the political culture of the empire.

Christianity gained importance in late antiquity. Tradition associated the apostle Philip with martyrdom at Hierapolis, and a large octagonal Martyrion was built above the city. Hierapolis became a bishopric, while baths and temples were adapted to new uses. Earthquake, changing trade patterns, and warfare reduced the settlement over centuries. Seljuk occupation added another historical layer, but the urban center was largely abandoned after a major medieval earthquake. Travertine deposits continued to form as buildings collapsed and the ancient water system deteriorated.

Modern hotels and uncontrolled bathing once damaged and discolored the terraces by diverting water and allowing vehicles onto the formations. Management changes removed intrusive development, restricted bathing to designated areas, and rotate spring flow to maintain the white surface. Italian-led archaeological work has excavated and restored the theater, Plutonium, streets, tombs, and Christian monuments, while the Roman bath houses the site museum. UNESCO inscribed Hierapolis-Pamukkale in 1988 as a combined natural and cultural property. Its significance depends on their interaction: geology created the water, landscape, economy, ritual, and preservation challenges of the ancient city.