The city was expanded with the booty from the 190 BC Battle of Magnesia where Antiochus the Great was defeated by the Roman ally Eumenes II. Following the Treaty of Apamea ending the Syrian War, Eumenes annexed much of Asia Minor, including Hierapolis.
Hierapolis became a healing centre where doctors used the thermal springs as a treatment for their patients. The city began minting bronze coins in the 2nd century BC. These coins give the name Hieropolis. It remains unclear whether this name referred to the original temple (ἱερόν, hieron) or honoured Hiera, the wife of Telephus, son of Heracles and the Mysian princess Auge, the supposed founder of Pergamon's Attalid dynasty. This name eventually changed into Hierapolis ("holy city"), according to the Byzantine geographer Stephanus on account of its large number of temples.
Hierapolis was first excavated by the German archaeologist Carl Humann during June and July 1887. His excavation notes were published in his 1889 book Altertümer von Hierapolis. His excavations were rather general and included a number of drilling holes. He would gain fame for his later discovery of the Pergamon Altar, which was reconstructed in the Pergamon Museum in Berlin.
After the large white limestone formations of the hot springs became famous again in the 20th century, it was turned into a tourist attraction named "Cotton Castle" (Pamukkale). The ancient city was rediscovered by travellers, but also partially destroyed by new hotels that were built there. These buildings have been removed in recent years; however, the hot water pool of one hotel was retained, and it is possible to swim amongst ancient stone remains.
Excavations began in earnest in 1957 when Italian scientists, led by Paolo Verzone, began working on the site. These studies continued into 2008 when a restoration of the site began. Large columns along the main street near the gate named for Domitian were erected again. A number of houses from the Byzantine period were also unearthed, including an 11th-century courtyard house. Many statues and friezes were transported to museums in London, Berlin, and Rome. In 1970, the Hierapolis Archaeology Museum was built on the site of the former Roman baths.
The Roman Bath, one of the biggest buildings of Hierapolis antique city, has been used as the site of the Hierapolis Archaeology Museum since 1984. In this museum, alongside the historical artifacts which were found in Hierapolis, there are some artifacts from Laodiceia, Colossae, Tripolis, Attuda and other towns of the Lycos valley. In addition to these, the museum has a large section devoted to artifacts found at Beycesultan Hüyük and which includes some of the most beautiful examples of Bronze Age craft.
Artifacts which have come from the Caria, Pisidia and Lydia regions are also on display in this museum. The museum's exhibition space consists of three closed areas of the Hierapolis Bath and open areas in the eastern side, which are known to have been used as the library and the gymnasium. The artifacts in the open exhibition space are mostly marble and stone.