Hastings' Dictionary of the New Testament 
Hierapolis was a city in the province of Asia, picturesquely situated on a broad terrace in the mountain range which skirts the N. side of the Lycus valley. On the S. side, 6 miles away, Laodicea was plainly visible, while Colossae lay hidden from view 12 miles to the S.E. Differing widely in history and character, these three cities were evangelized together soon after the middle of the 1st century. Hierapolis was probably an old Lydian city, but in the Roman period it was always regarded as Phrygian. A change in the spelling of the name is significant. While the older form-Hieropolis, the city of the hieron -limits the sanctity to the shrine, the later form-Hierapolis, the sacred city-conveys the idea that the whole place was holy.
In such an environment Christianity had to contend not merely with a superficial Hellenic culture, but with a deep-rooted native superstition. Politically of little account, Hierapolis was important as the home of an ancient Anatolian nature-worship, the cult of Leto and her son Sabazios. The striking physical phenomena of the place were clear indications to the primitive mind of the dreaded presence of a numen which required to be propitiated. The numerous hot streams tumbling down the side of the hill on which the city stood are strongly impregnated with alum, and the snow-white incrustations which cover the rocky terraces present the appearance of ‘an immense frozen cascade, the surface wavy, as of water in its headlong course suddenly petrified’ (R. Chandler, Travels in Asia Minor 3, 1817, p. 287). From a hole in the ground-probably filled up by Christians after a.d. 320-there issued fumes of mephitic vapour, which seemed to come from Hades, so that the awe-inspiring spot was called the Plutonion or Charonion (Strabo xiii. iv. 4). On account of its marvellous hot springs-regarded as a divine gift-the city was associated with the medicinal art of aesculapius, and under the Empire it became a famous health resort. It was the birth-place of Epictetus the Stoic.
Hierapolis is mentioned once in the NT ( Colossians 4:13), as a city causing grave concern to Epaphras, who was apparently the founder and first pastor of its church. The cities of the Lycus valley no doubt received the gospel at the time of St. Paul’s prolonged mission in Ephesus, the city from which the light radiated over the whole province of Asia ( Acts 19:10; Acts 19:26). Having acted as St. Paul’s delegate in the Lycus valley ( Colossians 1:7 [Revised Version]), Epaphras knew that the Apostle regarded its churches as in a manner his own, and after some years of strenuous labour the ‘faithful minister of Christ’ made a journey from Asia to Home to seek counsel and help in dealing with errors of doctrine and practice which threatened to undo his work.
There is a trustworthy tradition which connects the name of Philip the Apostle with Hierapolis. Polycrates, bishop of Ephesus towards the end of the 2nd cent.-as quoted by Eusebius ( HE [Note: E Historia Ecclesiastica (Eusebius, etc.).]iii. 31)-states that Philip, ‘one of the twelve,’ was among ‘the great lights of Asia,’ and that he was ‘buried at Hierapolis along with his two virgin daughters.’ Theodoret ( Commentary on Psalms 116) says that ‘the Apostle Philip controverted the error of the Phrygians.’ St. John is also believed to have preached at Hierapolis, and the progress of Christianity there was represented as the victory over the Echidna or serpent of aesculapius, which was identified with Satan. Hierapolis was made a metropolis by Justinian. The ruins of the city are extensive and well-preserved. The theatre is one of the finest in Asia Minor. The white terrace now bears the fanciful name of ‘Cotton Castle’ ( Pambuk-Kalessi ).
Literature.-W. J. Hamilton, Researches in Asia Minor , 1842, i. 507ff.; T. Lewin, Life and Epistles of St. Paul 3, 1875, i. 356f., W. M. Ramsay, Hist. Geog. of Asia Minor , 1890, p. 84, and Cities and Bishoprics of Phrygia , i.  84-120.
Hastings' Dictionary of the Bible 
HIERAPOLIS (‘holy city’) is mentioned in the Bible only in Colossians 4:13 , in association with the neighbouring towns Laodicea and ColossÃ¦. All three were situated in the valley of the Lycus, a tributary of the MÃ¦ander, in Phrygia, Hierapolis on the north side being about 6 miles from the former and 12 miles from the latter. (The best map of this district is at p. 472 of Ramsay’s Church in the Roman Empire .) It probably belonged originally to the tribe HydrelitÃ¦, and derived its title from the medicinal hot springs there, which revealed plainly to the ancient mind the presence of a divinity. The water is strongly impregnated with alum, and the calcareous deposit which it forms explains the modern name Pambuk-Kalessi (Cotton Castle). Another sacred attribute of the city was a hole, about the circumference of a man’s body, from which noxious vapours issued: Strabo (in the time of Augustus) had seen sparrows stifled by them. The city owed all its importance in NT times to its religious character. It had not been visited by St. Paul, but derived its Christianity from his influence (cf. Acts 19:10 and Col.). Legend declares that the Apostles Philip and John preached there, and this appears trustworthy. The fight between native superstition and the enlightenment brought by Christianity must have been very bitter. The city remained important throughout the Empire, and was the birthplace of Epictetus, the Stoic.
American Tract Society Bible Dictionary 
A city of Phrygia, situated on its western border, near the junction of the rivers Lycus and Meander, and not far from Colosses and Laodicea. It was celebrated for its warm springs and baths. A Christian church was early established here, and enjoyed the ministrations of the faithful Epaphras, Colossians 4:12,13 . The city is now desolate, but its ruins still exhibit many traces of its ancient splendor. Among them are the remains of three churches, a theatre, a gymnasium, and many sepulchral monuments. The white front of the cliffs, above which the city lay, has given it its present name of Pamluke-kaleh, the Cotton Castle.
People's Dictionary of the Bible 
Hierapolis ( Hî'E-R Ăp'O-L Ĭs ), Sacred City. A city in Proconsular Asia, Colossians 4:13, near the river Lycus, and in sight of Laodicea, which was about 5 miles to the south. It stood on a high bluff, with a high mountain behind it. In the city was the famous temple of Pluto, remains of which are still to be seen. The ruins of the city are extensive, as temples, churches, a triumphal arch, a theatre, gymnasium, baths, and highly ornamented sarcophagi.
Fausset's Bible Dictionary 
Colossians 4:13. Associated as the seat of a church with the neighbouring Colossae and Laodicea; on a height between the rivers Lycus and Meander, within a few miles of one another; the three churches were probably all founded by Epaphras. Now Pambouk Kalessi. Hot calcareous springs are near, which have deposited curious encrustations. There is a frozen cascade, the surface wavy, as of water suddenly petrified. A mephitic cavern, Plutonium, was in ancient times connected with the worship of Cybele, from from whence the city was designated Hierapolis, "the sacred city."
Smith's Bible Dictionary 
Hi-erap'olis. (Holy City). A city of Phrygia, situated above the junction of the rivers Lycus and Maeander, near Colossae and Laodicea mentioned only in Colossians 4:13, as the seat of a church, probably, founded by Epaphras.
Morrish Bible Dictionary 
City of Phrygia in Asia Minor, for the saints of which Epaphras had a great zeal, or for whom he laboured much. Colossians 4:13 . Now called Pambuk Kalesi, 37 58' N, 29 11' E . It is remarkable for its hot calcareous springs, which have deposited curious incrustations.
Easton's Bible Dictionary 
Holman Bible Dictionary 
Cyclopedia of Biblical, Theological and Ecclesiastical Literature 
( ῾Ιεράπολις , Sacred City), a city of Phrygia, situated above the junction of the rivers Lycus and Maeander, not far from Colossse and Laodicea, where there was a Christian church under the charge of Epaphras as early as the time of the apostle Paul, who commends him for his fidelity and zeal ( Colossians 4:12-13). The place is visible from the theatre at Laodicea, from which it is five miles distant northward. Its association with Laodicea and Colossee is just what we should expect, for the three towns were all in the basin of the Mseander, and within a few miles of one another. It is probable that Hierapolis was one of the "illustres Asiue urbes" (Tacitus, Ann. 14, 27) which, with Laodicea, were simultaneously desolated by an earthquake about the time when Christianity was established in this district. There is little doubt that the church of Hierapolis was founded at the same time with that of Colossae, and that its characteristics in the apostolic period were the same. Smith, in his journey to the Seven Churches (1671), was the first to describe the ancient sites in this neighborhood.
He was followed by Pococke and Chandler; and more recently by Richter, Cockerell, Hartley, Arundel, etc. The place now bears the name of Pambuk-Kalek (Cotton-Castle), from the white appearance of the cliffs of the mountain on the lower summit, or, rather, an extended terrace, on which the ruins are situated. It owed its celebrity, and probably the sanctity indicated by its ancient name, to its very remarkable thermal springs of mineral water (Dio Cass. 68, 27; Pliny, Hist. Nat. 2, 95), the singular effects of which, in the formation of stalactites and incrustations by its deposits, are shown in the accounts of Pococke (2, pt. 2, c. 13) and Chandler (Asia Minor, c. 68) to have been accurately described by Strabo (13, 629). A great number and variety of sepulchers are found in the approaches to the site, which on one side is sufficiently defended by the precipices overlooking the valleys of the Lycus and Maeander, while on the other sides the town walls are still observable. The magnificent ruins clearly attest the ancient importance of the place.
The main street can still be traced in its whole extent, and is bordered by the remains of three Christian churches, one of which is upwards of 300 feet long. About the middle of this street, just above the mineral springs, Pococke, in 1741, thought that he distinguished some remains of the Temple of Apollo, which, according to Damascus, quoted by Photius (Biblioth. p. 1054), was in this situation. But the principal ruins are a theatre and gymnasium, both in a state of uncommon preservation; the former 346 feet in diameter, the latter nearly filling a space 400 feet square. Strabo (loc. cit.) and Pliny (Hist. Nat. 5, 29) mention a cave called the Plutonium, filled with pestilential vapors, similar to the celebrated Grotto del Cane in Italy. High up the mountain-side is a deep recess far into the mountain; and Mr. Arundell says that he should have supposed that the mephitic cavern lay in this recess, if Mr. Cockerell had not found it near the theatre, the position anciently assigned to it; and he conjectures that it may be the same in which Chandler distinguished the area of a stadium (Arundell, Asia Minor, 2, 210). The same writer gives, from the Oriens Christianus, a list of the bishops of Hierapolis down to the time of the emperor Isaac Angelus. (See Col. Leake's Geogr. of Asia Minor, p. 252, 253; Hamilton's Res. in Asia Minor, 1, 514, 517 sq.; Fellows, Lycia, p. 270; Asia Minor, p. 283 sq.; Cramer's Asia Minor, 2, 37 sq.).
International Standard Bible Encyclopedia 
hē - ẽr - ap´ō̇ - lis ( Ἱεράπολις , Hierápolis , "sacred city"): As the name implies, Hierapolis was a holy city. It was situated 6 miles from Laodicea and twice that distance from Colosse, on the road from Sardis to Apamea. Though its history is not well known, it seems to have been of Lydian origin, and once bore the name of Kydrara. The Phrygian god Sabazios was worshipped there under the name Echidma, and represented by the symbol of the serpent. Other local deities were Leto and her son Lairbenos. Though called the holy city, Hierapolis was peculiarly regarded as the stronghold of Satan, for there was a Plutonium, or a hole reaching far down into the earth, from which there issued a vapor, even poisoning the birds flying above. It is supposed that upon a stool, deep in the Plutonium, a priest or priestess sat, and, when under the influence of the vapor, uttered prophecies valuable to those who sought them. Though a stronghold of Satan, Hierapolis early became a Christian city, for, according to Colossians 4:13 , the only place where it is mentioned in the New Testament, a church was founded there through the influence of Paul while he was at Ephesus. Tradition claims that Philip was the first evangelist to preach there, and it also claims that he and his two unmarried daughters were buried there; a third who was married, was buried at Ephesus. Several of the early Christians suffered martyrdom at Hierapolis, yet Christianity flourished, other churches were built, and during the 4th century the Christians filled the Plutonium with stones, thus giving evidence that the paganism had been entirely supplanted by the church. During the Roman period, Justinian made the city a metropolis, and it continued to exist into the Middle Ages. In the year 1190 Frederick Barbarossa fought with the Byzantines there.
The modern town is called Pambuk Kalessi , or cotton castle, not because cotton is raised in the vicinity, but because of the white deposit from the water of the calcareous springs. The springs were famous in ancient times because they were supposed to possess Divine powers. The water is tepid, impregnated with alum, but pleasant to the taste. It was used by the ancients for dyeing and medicinal purposes. The deposit of pure white brought up by the water from the springs has heaped itself over the surrounding buildings, nearly burying them, and stalactite formations, resembling icicles, hang from the ruins. The ruins, which are extensive, stand on a terrace, commanding an extensive view, and though they are partly covered by the deposit, one may still trace the city walls, the temple, several churches, the triumphal arch, the gymnasium and baths, and the most perfect theater in Asia Minor. Outside the walls are many tombs.
Kitto's Popular Cyclopedia of Biblial Literature 
Hierap´olis, a city of Phrygia, not far from Colosse and Laodicea, where there was a Christian church under the charge of Epaphros, as early as the time of St. Paul, who commends him for his fidelity and zeal . The place is visible from the theater at Laodicea, from which it is five miles distant northward.
The place now bears the name of Pamluck-kale (Cotton-castle), from the white appearance of the cliffs of the mountain on the lower summit, or rather an extended terrace, on which the ruins are situated. It owed its celebrity, and probably the sanctity indicated by its ancient name (Holy City), to its very remarkable springs of mineral water, the singular effects of which, in the formation of stalactites and incrustations by its deposits, are shown in the accounts of Pococke and Chandler, to have been accurately described by Strabo. A great number and variety of sepulchers are found in the different approaches to the site, which on one side is sufficiently defended by the precipices overlooking the valleys of the Lycus and Mæander, while on the other sides the town walls are still observable. The magnificent ruins clearly attest the ancient importance of the place.
The Nuttall Encyclopedia 
1, an ancient city of Syria Cyrrhestica, now in ruins, situated between Antioch and Mesopotamia, 14 m. W. of the Euphrates; had considerable commercial importance, and was famous for its great temple of Astarte. 2, A city of ancient Phrygia, 5 m. N. of Laodicea; the birthplace of Epictetus, and where Paul founded a church; was celebrated for its hot springs.
- Hierapolis from Hastings' Dictionary of the New Testament
- Hierapolis from Hastings' Dictionary of the Bible
- Hierapolis from American Tract Society Bible Dictionary
- Hierapolis from People's Dictionary of the Bible
- Hierapolis from Fausset's Bible Dictionary
- Hierapolis from Smith's Bible Dictionary
- Hierapolis from Morrish Bible Dictionary
- Hierapolis from Easton's Bible Dictionary
- Hierapolis from Holman Bible Dictionary
- Hierapolis from Cyclopedia of Biblical, Theological and Ecclesiastical Literature
- Hierapolis from International Standard Bible Encyclopedia
- Hierapolis from Kitto's Popular Cyclopedia of Biblial Literature
- Hierapolis from The Nuttall Encyclopedia