Hastings' Dictionary of the Bible 
Pergamum , or Pergamus , was an ancient city of Mysia, the seat of an independent kingdom from about b.c. 280 to b.c. 133, and the capital of the Roman province of Asia from b.c. 133 until the 2nd cent. a.d. It lay in the Caicus valley about 15 miles from the sea, and its acropolis rose between two tributary streams 3 miles N. of the Caicus. As the capital of a kingdom, Pergamus had acquired a somewhat factitious importance. It stood on no great trade route, and under the Romans it slowly lost all but the official pre-eminence in the province. Its kings had been champions of Greek civilization and arts, and it still remained a centre of conservative culture. But Ephesus was now the centre of trade, and it was at Ephesus that West and East met together, creating a medley of all philosophies and all religions. At Pergamus there were splendid temples of Zeus and Athene, where these gods were worshipped in the ordinary Greek way, but others also of Dlonysos and Asklepios.
The only allusion to Pergamus in the NT is in the Apocalypse, where ( Revelation 1:11; Revelation 2:12 ) it is included among the seven churches of Asia. The message to it speaks of Pergamus as the place ‘where Satan’s seat is.’ While it is possible that this refers to it as the chief seat of heathen worship in general, it is more probable that it refers to the worship of Rome and Augustus, participation in which had become a test of loyalty, and therefore a frequent ground of Christian martyrdom. Christians would be brought to Pergamus for trial from any northern part of the province, and the mention of one martyr, Antipas , as having suffered there does not prove that he belonged to Pergamus. The Church at Pergamus is charged with having ‘them that hold the doctrine of Balaam , who taught Balak to cast a stumbling-block before the children of Israel, to eat things sacrificed unto idols, and to commit fornication’; and also ‘them that hold the doctrine of the Nic olaitans.’ We must gather from this that a definite section of the church at Pergamus maintained that, Inasmuch as heathen ceremonies’ meant nothing’ (cf. Co 8:4; 10:19), they were at liberty to join in idolatrous feasts, and thus to maintain their social position and justify their loyalty in the sight of the law. The allusion in 2:17 to ‘a w hite stone , and in the stone a new name written,’ may be an allusion to a practice of keeping secret a new name taken at baptism in a place where it was dangerous to be known as a Christian. From its official and religious character there can be little doubt that Antipas was but one of many martyred at Pergamus.
Pergamus was the seat of a bishopric, but its subsequent history is obscure. It retains its name in the form Bergama . The German Government has been conducting excavations on the site since 1878, and in 1901 a Pergamon Museum was opened in Berlin. The name of Pergamus survives in the word ‘parchment,’ i.e . Pergamena. It is said that king Eumenes, the founder of the library, invented the use of this preparation of sheep-skin or goat-skin for the purposes of writing.
A. E. Hillard.
Bridgeway Bible Dictionary 
The town of Pergamum was in the province of Asia, on the west coast of Asia Minor ( Revelation 1:4; Revelation 1:11; for map see Asia ). The Bible does not record how or when the church there was founded, but it does mention difficulties that the church experienced towards the end of the first century. The difficulties were mainly connected with the religious system known as Emperor worship, which in the province of Asia had its headquarters in Pergamum (cf. Revelation 2:13). (Concerning Emperor worship see Rome .)
On the whole the Christians in Pergamum stood firm and refused to join in the Emperor worship. At least one of their number was martyred ( Revelation 2:12-13). There were some, however, who taught and practised Nicolaitan teaching, which encouraged Christians to join in idolatrous feasts and to practise immorality. Jesus declared he would judge those who denied him in this way, and reward those who refused to compromise with the State religion ( Revelation 2:14-17).
Smith's Bible Dictionary 
Per'gamum. In the Revised Version for Pergamos . Revelation 1:11. Pergamum is the form usual in the classic writers.
Holman Bible Dictionary