The guide to Hierapolis in Phirygia (Pamukkale) is intended as an introduction to the city and its Hellenistic and Roman monuments for the general public. The Italian Archaeological Mission, in close collaboration with the Turkish authorities, has been developing a substantial programme of excavation and conservation since 1957. Hierapolis is characterised by the largest cemetery in Asia Minor, with innumerable sarcophagi, funerary chapels and large barrows or tumuli. The hot water springs created the natural travertine basins that favoured the construction of large Roman baths. The religious centre of the city was the Sanctuary of Apollo, renowned for its alphabetic oracle, which rose above the cave of the Plutonion, one of the entrances to the underworld. In Christian times, the city was the centre of pilgrimage to the tomb of the Apostle Philip, martyred at Hierapolis. A monumental octagonal building, sited on the hill dominating the city, was erected in his honour.