Hierapolis (hīərăp`əlĭs), ancient city of Phrygia, W Asia Minor, 7 mi (11.3 km) N of Laodicea and on a plateau 500 ft (152 m) above the Lycus valley (in present-day Turkey). Devoted to the worship of Leto in ancient times, it became an early seat of Christianity (Colossians 4.13). The Romans greatly enlarged and improved the city, building a large theater and numerous baths about the hot springs for which the site is famous. Near the city was a deep chasm called the Plutonium, which the ancients thought led to the nether regions; the fissure no longer exists. Extensive ruins survive from the Roman and Christian periods.