The seven churches of Rev. chapt. 1 - 3 were located in and surrounded the capital city of Asia Minor, the “seat of Satan” in Pergamos (var. Pergamum) (Rev. 2:13.) The “seat of Satan” was a reference to the center of idolatry, as Pergamos practiced sun worship, which originated from Babylonian idolatry, and their priests used the same vestments and title of “pontiff.”
Their people were called “The Temple-keepers of Asia.” They had several gods, the chief of which was Zeus. The last leader of Pergamum gifted his title of Pontifex Maximus to Rome in 133 BC. The rulers and emperors of Rome used the title until 382 AD, when Emperor Gratian refused it as being un-Christian. But, it is interesting to note that it is still used today by the Pope.
Excerpt from Studies in Revelation by Hamption Keathly III, 1997, p. 63:
"Pergamum was very wealthy, the center of emperor worship with many temples devoted to idolatry. This was the place ‘where Satan’s throne is’ (Rev. 2:13). The phrase has been applied to the complex of pagan cults, of Zeus, Athena, Dionysus and Asclepius (Esculapius), established by the Attalid kings, that of Asclepius Soter (the ‘saviour,’ ‘healer’) being of special importance. These cults are illustrative of the religious history of Pergamum, but “Satan’s throne” could be an allusion to emperor worship. This was where the worship of the divine emperor had been made the touchstone of civic loyalty under Domitian.
Here was the magnificent temple of Esculapius, a pagan god whose idol was in the form of a serpent. The inhabitants were known as the chief temple keepers of Asia. When the Babylonian cult of the Magians was driven out of Babylon, they found a haven in Pergamum. "
And:
"The title of the Magian high priest was “Chief Bridge Builder” meaning the one who spans the gap between mortals and Satan and his hosts. In Latin this title was written “Pontifex Maximus,” the title now used by the Pope. This title goes all the way back to Babylon and the beginnings of the mother-child cult under Nimrod of Genesis 10 and his wife Sumerimus. Later, Julius Caesar was elected Pontifex Maximus and when he became Emperor, he became the supreme civil and religious ruler and head of Rome politically and religiously with all the power and functions of the Babylonian pontiff." Source: "The Message to Pergamum" here
From The Seven Golden Candlesticks by Henry Baker Tristram. p. 63
"Like Ephesus, it boasted on its coins and in inscriptions to be a temple-keeper, and like other Asiatic Greeks, we may be certain that the Pergamenes were devoted to a sensuous and licentious worship....The tutelary diety of Pergamu was AEsculapius, the god of healing.....In his honor, a living serpent was kept and fed in the temple, while the serpent-worship was so marked a character of the place, that we find this reptile engraved on many of its coins." Source: here
The seven churches of Asia had to be strong, and fight to resist temptation, to remain faithful to Christ, and not mix with pagan idolatry. That was one of the reasons for the constant encouragement in all of the letters of the apostles / disciples for the people to continue in their belief in the Lord and the gospel of Christ.
Satan's main tool was to deceive the people to turn them away from our heavenly Father, to worship anything / anyone other than our Creator, and places of idol worship were the work of Satan, thus the seat of Satan.
ADDENDUM:
Excerpt from Acropolis of Pergamum:
Pergamum inscription on white stone
The people of Pergamum were known as the "Temple-keepers of Asia." The city had three temples dedicated to the worship of the Roman emperor, another for the goddess Athena, and the Great Altar of Zeus, the king of the Greek gods. Many scholars believe this altar is the “Throne of Satan” mentioned in the book of Revelation.
“That word ‘throne’ was used in a personal private residence, and it was a chair for the lord of the house, the master of the house,” says Renner. “The very fact that Jesus would use this word means that Satan felt at home there. He sat on a throne there. It was his territory. He was the master of that house.”
The city also had a healing center called the Asklepion, built in honor of Asklepios, the Greek serpent-god. In the first century, this was a cross between a hospital and a health spa, where patients could get everything from a mud bath to a major surgery. Even the emperors came all the way from Rome to be treated here, but this was no ordinary doctor's visit." Source: here
The title assumed by the bishop of the RCC is pagan in origin, and predates Augustus' resurrection of it as part of the Roman Imperial titles.
Excerpt from Anchoring Pontifical Authority:
Augustus, the first Roman in history to combine the novel position of emperor with that of pontifex maximus, recalled in his Res Gestae: “By the passage of new laws I restored many traditions of our ancestors which were then falling into disuse, and I myself set precedents in many things for posterity to imitate.” 59 Augustus' words capture antique Roman society well, where conservatism and innovation proved a winning combination. Similarly, the earliest pope in history to have himself presented as pontifex maximus understood the synergy of old and new joined together, and the necessity to have the innovative use of this title embedded or anchored in tradition in order for it to meet with approval from the various groups in society. Thus, the title pontifex maximus as appropriated by popes of the past was anchored in the tradition of imperial Roman titulature." Source: here
The pagan title was picked up by the Roman bishops and then transferred to the Pope later.
Excerpt from The Title Pontifex Maximus:
"Of course Christ didn't appoint Peter to be the Pontifex Maximus. And of course the early Church Fathers spoke of the Pontifex Maximus in such derogatory, paganistic ways. Because when the early Fathers were writing, the Pontifex Maximus was the head of the Roman pagan religion, and the Roman Empire itself was pagan. As any student of Roman history knows, the Pontifex Maximus was an imperial office, usually held by the Emperor himself, which made one the "chief priest" of the Roman "state cult."' Source: Biblical Catholic
Excerpt from The Title Pontifex Maximus:
"he papal title Pontifex Maximus can be traced back in different forms to the ancient Chaldean times. When Medo-Persia conquered Babylon, the Babylonian religion was maintained, but after a revolt of the priesthood, the priests of Babylon were driven out of Medo-Persia, and established themselves at Pergamum, taking with them their titles and vestures.
The last pontiff king of Pergamum was Attalus III, who bequeathed his title to the emperor of Rome in 133 BC. In the fourth century AD, Christian emperor Gratian refused the title, and in the year 431 AD, the title was taken over by Damascus, bishop of Rome." Source: here
The last king of Pergamum, Attalus III bequeathed the territory and treasure of Pergamum to Rome to avoid a civil war. Thereafter, Pergamum became a province of Rome. Source: Livius
The seat of Satan in the book of Revelation was the seat of idol worship in Asia Minor where the letter to the church at Pergamum was sent. The title Pontifex Maximus was the title used by pagan idol worshipers,and taken up by the emperors of Rome to combine all authority under the emperor for both cult worship and political rule.
Further, this site is not about specific religions, but about the Bible, the word of God. Any teaching that contradicts the Bible should be freely discussed, and not censored. The background of Pergamum is essential to understanding what Christ was telling the people in that letter in Rev.
Further sources:
Bruce Gore - Apocalypse in Space and Time, Part 2 here
Bruce Gore - Apocalypse in Space and Time, Part 17 here