Hierapolis in Pamukkale, Turkey

“Hierapolis, the “Sacred City,” is located at present-day Pamukkale in south central Turkey.  In the first century it was part of the tri-city area of Laodicea, Colossae, and Hierapolis.  This connection between the cities lies behind Paul’s reference to Hierapolis and Laodicea in his epistle to the Colossians (Col 4:13).  Before AD 70 Phillip (either the apostle or the evangelist) moved to Hierapolis, where he was believed to have been martyred.”

http://www.bibleplaces.com/hierapolis/