Hierapolis

Hierapolis (modern Pamukkale), together with Colossae and Laodicea formed three major cities in the Lycus River Valley. The only mention of Hierapolis in the Bible was in Colossians 4:12-13. Epaphras, a native of Colossae was mentioned by Paul:

12 Epaphras, who is one of you and a servant of Christ Jesus, sends greetings. He is always wrestling in prayer for you, that you may stand firm in all the will of God, mature and fully assured. 13 I vouch for him that he is working hard for you and for those at Laodicea and Hierapolis.(NIV)

While there is not much historical data on Epaphras, it is likely that he started churches in the Lycus River Valley including in Hierapolis itself.

The most prominent feature of Hierapolis are the white limestone cliffs which are visible from a long distance. These white cliffs are called cotton castle or Pamukkale which gives the modern town its name. It has been designated as one of UNESCO's World Heritage site.

The ancient city of Hierapolis was associated with Philip. However no one was sure whether it is Philip the Evangelist or Philip the apostle, one of the twelve disciples of Jesus. Philip the Evangelist was one of the seven men chosen to help the Twelve (Acts 6:1-6)

AC 6:1 In those days when the number of disciples was increasing, the Grecian Jews among them complained against the Hebraic Jews because their widows were being overlooked in the daily distribution of food. 2 So the Twelve gathered all the disciples together and said, "It would not be right for us to neglect the ministry of the word of God in order to wait on tables. 3 Brothers, choose seven men from among you who are known to be full of the Spirit and wisdom. We will turn this responsibility over to them 4 and will give our attention to prayer and the ministry of the word."

AC 6:5 This proposal pleased the whole group. They chose Stephen, a man full of faith and of the Holy Spirit; also Philip, Procorus, Nicanor, Timon, Parmenas, and Nicolas from Antioch, a convert to Judaism. 6 They presented these men to the apostles, who prayed and laid their hands on them.

This Philip is known to have four virgin daughters who were also prophets (Acts 21:8-9).

8 Leaving the next day, we reached Caesarea and stayed at the house of Philip the evangelist, one of the Seven. 9 He had four unmarried daughters who prophesied.

There are traditions that this Philip was buried in Hierapolis along with his four virgin daughters. However there are other traditions to indicate that the Philip buried in Hierapolis was one of the Twelve. This Philip the Apostle was martyred by being hung upside down by his ankles from a tree. A martyrion to Philip the Apostle was erected in Hierapolis.

There are many Greco-Roman, Byzantine and medieval ruins at the archaeological site of Hierapolis.

The above map was scanned from Fant & Reddish, A guide to Biblical sites in Greece and Turkey, 210

Headlines from the Daily Mail (UK) Apr 2, 2013 on the discovery of the Plutonium

Is this the Gate of Hell? Archaeologists say temple doorway belching noxious gas matches ancient accounts of 'portal to the underworld'

From Wiki:

Next to this temple and within the sacred area is the oldest local sanctuary, Pluto's Gate, a shrine to Pluto (Ancient Greek: Πλουτωνειον, ploutoneion; Latin: plutonium). This plutonium was described by several ancient writers, including Strabo, Cassius Dio, and Damascius. It is a small cave just large enough for one person to enter through a fenced entrance, beyond which stairs go down and from which emerges suffocating carbon dioxide gas caused by subterranean geologic activity. Behind the 3 square metres (32 sq ft) roofed chamber is a deep cleft in the rock, through which fast-flowing hot water passes while releasing a sharp-smelling gas.

During the early years of the town, castrated priests of Cybele descended into the plutonium, crawling over the floor to pockets of oxygen or holding their breath. Carbon dioxide is heavier than air and so tends to settle in hollows. The priests would then come up to show that they were miraculously immune to the gas and infused with divine protection.

An enclosed area of 2,000 square metres (22,000 sq ft) stood in front of the entrance. It was covered by a thick layer of suffocating gas, killing anyone who dared to enter it. The priests sold birds and other animals to the visitors, so that they could try out how deadly this enclosed area was. Visitors could (for a fee) ask questions of Pluto's oracle. This provided a considerable source of income for the temple. The entrance to the plutonium was walled off during the Christian times and has just been recently unearthed

source: http://en.wikipedia.org/wiki/Hierapolis