Pergamos

the chief city of Mysia, in Asia Minor. One of the "seven churches" was planted here (Rev 1:11; 2:17). It was noted for its wickedness, insomuch that our Lord says "Satan's seat" was there. The church of Pergamos was rebuked for swerving from the truth and embracing the doctrines of Balaam and the Nicolaitanes. Antipas, Christ's "faithful martyr," here sealed his testimony with his blood.

This city stood on the banks of the river Caicus, about 20 miles from the sea. It is now called Bergama, and has a population of some twenty thousand, of whom about two thousand profess to be Christians. Parchment (q.v.) was first made here, and was called by the Greeks pergamene, from the name of the city.

EBD - Easton's Bible Dictionary