“To the angel of the assembly in Pergamum write:” Rev 2:12.

“The early people of the town were descendants of Greek colonists, and as early as 420 bc they struck coins of their own. … Attalus I (241-197 BC) … adorn[ed] the city with beautiful buildings until it became the most wonderful city of the East … Art and literature were encouraged, and in the city was a library of 200,000 volumes which later Antony gave to Cleopatra. The books were of parchment which was here first used; hence, the word ‘parchment,’ which is derived from the name of the town Pergamos. … When in 133 BC … the last king … died, he gave his kingdom to the Roman government. … and the Roman province of Asia was formed, and Pergamos was made its capital.   … Of the structures which adorned the city, the most renowned was the altar of Zeus, which was 40 ft. in height, and also one of the wonders of the ancient world. … A title which it bore was ‘Thrice Neokoros,’ meaning that in the city three temples had been built to the Roman emperors, in which the emperors were worshipped as gods. Smyrna, a rival city, was a commercial center, and as it increased in wealth, it gradually became the political center. Later, when it became the capital, Pergamos remained the religious center. As in many of the towns of Asia Minor, there were at Pergamos many Jews, and in 130 BC the people of the city passed a decree in their favor. Many of the Jews were more or less assimilated with the Greeks, even to the extent of bearing Greek names.”

“Pergamos; Pergamum,” International Standard Bible Encyclopedia.

“Pergamum continued to rank for two centuries as the capital, and subsequently, with Ephesus and Smyrna, as one of the three great cities of the province; and the devotion of its former kings to the Roman cause was continued by its citizens; who erected on the Acropolis a magnificent temple to Augustus. … Pergamum was the chief centre of the imperial cult under the early empire, and, in W. M. Ramsay’s opinion, was for that reason referred to in Rev. ii. 13 as the place of ‘Satan’s throne.’ It was also an early seat of Christianity, and one of the seven churches.”

“Pergamum,” The Encyclopaedia Britannica, Vol. 21, p. 143.

Sexual immorality and eating things sacrificed to idols were part and parcel of pagan idolatry.

“The special enticements to idolatry as offered by these various cults were found in their deification of natural forces and their appeal to primitive human desires, especially the sexual … Baal and Astarte worship, which was especially attractive, was closely associated with fornication and drunkenness (Amos 2:7 , Amos 2:8; compare 1 Kings 14:23 f), and also appealed greatly to magic and soothsaying (e.g. Isaiah 2:6; Isaiah 3:2; Isaiah 8:19 ).”

“Idolatry,” International Standard Bible Encyclopedia.

“It seems strange to a modern reader that with these ceremonial prohibitions [against idolatry] should be connected the strictly moral prohibition of fornication. … no heathen moralist, not even Socrates, or Plato, or Cicero, condemned fornication absolutely. It was sanctioned by the worship of Aphrodite at Corinth and Paphos, and practiced to her honor by a host of harlot-priestesses! … Hence the author of the Apocalypse also closely connects the eating of meat offered to idols with fornication, and denounces them together.”

Philip Schaff, History of the Christian Church, Vol. 1, pp. 294.

“Ancient Near Eastern societies … featured many shrines and temples or ‘houses of heaven’ dedicated to various deities. According to the 5th-century BC historian Herodotus, the rites performed at these temples included … what scholars later called sacred prostitution. … The Hebrew Bible uses two different words for prostitute, zonah (זנה)‎ and kedeshah (or qedesha) (קדשה)‎. The word zonah simply meant an ordinary prostitute or ‘loose woman’. But the word kedeshah literally means ‘consecrated’ (feminine form), from the Semitic root q-d-sh (קדש)‎ meaning ‘holy’ or ‘set apart’. Whatever the cultic significance of a kedeshah to a follower of the Canaanite religion, the Hebrew Bible makes it clear that cultic prostitution had no place in Judaism. Thus the Hebrew version of Deuteronomy 23:17-18 tells followers: ‘None of the daughters of Israel shall be a kedeshah, nor shall any of the sons of Israel be a kadesh. You shall not bring the hire of a prostitute (zonah) or the wages of a dog (kelev) into the house of the Lord your God to pay a vow, for both of these are an abomination to the Lord your God.’ Stephen O. Murray writes that biblical passages ban qdeshim and link them with gods and ‘forms of worship detested by orthodox followers of Yahweh’.”

“Sacred Prostitution,” Wikipedia.