The new kingdom was initially in a vassal-like relationship of nominal fealty to the Seleucid Empire, but exercised considerable autonomy and soon became entirely independent.

Philetaerus rose from humble origins to become a lieutenant of Lysimachus, one of Alexander the Great's generals (diadochi), who ruled a large state centered around Byzantium.

He contributed troops, money, and food to the city of Cyzicus, in Mysia, for its defense against the invading Gauls, thus gaining prestige and goodwill for him and his family.

[5] Early in his reign, he won a battlefield victory against the Galatians of Asia Minor (called Gauls by Pausanias) at the Battle of the Caecus River.

[6] This victory was a key to the legitimacy of Hellenistic kings, who styled themselves after Alexander the Great's legacy of military glories, and improved the standing and prestige of the kingdom.

Antiochus Hierax made alliances with other kings in Asia Minor, his base of power, including both the Galatians and the Cappadocians.

[8] With Antiochus Hierax's death, Attalus gained control over all Seleucid territories in Asia Minor north of the Taurus Mountains.

In 223 BC, Seleucus III crossed the Taurus, but was assassinated, and the general Achaeus assumed control of the Seleucid army.

Within two years, he had recovered the lost territories, taken parts of the traditional Pergamese heartland, and forced Attalus to retreat within the walls of Pergamon.

However, Achaeus himself turned on Antiochus III and proclaimed himself a king, perhaps because he was accused of intending to revolt anyway, or perhaps simply drunk with success.

[16] In 188 BC, after the war's end by the Treaty of Apamea, the Romans seized the possessions of the defeated Antiochus III in Asia Minor and gave Mysia, Lydia, Phrygia, and Pamphylia to the kingdom of Pergamon and Caria, Lycia and Pisidia, in the southwestern corner of Asia Minor, to Rhodes, another Roman ally.

[16] Eumenes II also successfully intervened in Seleucid politics, aiding Antiochus IV Epiphanes in his quest to take the throne from Heliodorus.

In 189 BC he led the Pergamene troops which flanked the Roman army under Gnaeus Manlius Vulso in the Galatian War.

[22] Two notable cults in early Pergamon were the cult of the Cabiri, a pantheon likely of original Phrygian or Thracian origin that became syncretized with Greek beliefs and mythology, and the Corybantes, worshippers of the mother goddess Cybele (possibly the Asia Minor equivalent of the Greek goddess Rhea).

[24] After the Pergamese expansion in size and prestige after the Treaty of Apamea, King Eumenes II embarked upon a vast building program in Pergamon to suit the capital's new prominence.

He expanded the Library of Pergamon that had probably been started by his father Attalus I, which adjoined the newly created Temple to Athena noted above.

Similarly, the Attalids implausibly claimed a link to Alexander the Great via Pergamus, a very marginal figure who was a son of Andromache and Neoptolemus.

According to the Attalids, Pergamus had founded the city of Pergamon and named it after himself, while they claimed Andromache was a distant ancestor of Olympias, Alexander's mother.

[25] Knowledge of the dates of the reigns of the Attalid kings are largely based on Strabo's Geography, with a few minor corrections by modern historians for apparent slips of the pen.

[26][27] A notable aspect of Attalid dynastic propaganda was the unity of the family and the avoiding of petty royal squabbles between siblings that consumed their neighbors in civil wars and assassinations.

Polybius has Philip V of Macedon praise the Attalids, his enemies, for their unity as instrumental to their success as he mourns the hatred between his own sons that brought down the Antigonid Macedonian kingdom.

While this dialogue was surely a literary invention, it seems accurate that the Attalid royal court avoided scandal and appealed well to the common citizenry.