Attalus won an important victory, the Battle of the Caecus River, over the Galatians, a group of migratory Celtic tribes from Thrace, who had been plundering and exacting tribute throughout most of Asia Minor for more than a generation.

The victory was celebrated with a triumphal monument at Pergamon (The Dying Gaul) and Attalus taking the surname "Soter" and the title of king.

Since the time of Philetaerus, the first Attalid ruler, the Galatians had posed a problem for Pergamon, indeed for all of Asia Minor, by exacting tributes to avoid war or other repercussions.

Around the 230s BC, the depiction of Philetaerus changed from a plain band to a diadem entwined with a laurel wreath, the symbol of victory, perhaps to celebrate the defeat of the Galatians.

[16] Pausanias wrote of a surely invented oracle's prophecy which foretold the great victory, allegedly created a generation earlier:[17] Then having crossed the narrow strait of the Hellespont, The destructive army of the Gauls shall pipe; they shall lawlessly Ravage Asia; and God shall make it yet worse For all who dwell by the shores of the sea For a little while.

[17] Pausanias writes that by "son of a bull", the oracle Phaennis "meant Attalus, king of Pergamon, who was styled bull-horned".

Three subsequent battles were fought and won against Antiochus Hierax's forces, which fought without support from the Gauls: in Hellespontine Phrygia, where Antiochus was perhaps seeking refuge with his father-in law, Ziaelas the king of Bithynia; near Sardis in the spring of 228 BC; and, in the final conflict of the campaign, in Caria at the Battle of the Harpasus, the Harpasus river being a tributary of the Maeander.

[23] Around 226–223 BC, Attalus erected a monument to his battlefield victories in the acropolis of Pergamon, dedicated to Zeus and Athena; a slight adjustment to the artwork on coinage also occurred.

This would later bring Attalus into conflict with Philip V of Macedon, king of Antigonid Macedonia and the preeminent power in the Aegean Sea region, in what would eventually become the First Macedonian War.

Attalus and Sulpicius then attended a meeting in Heraclea Trachinia of the Council of the Aetolians, at which the Roman argued against making peace with Philip.

[39] After his inglorious retreat, Attalus learned that Prusias I, king of Bithynia and a relative of Philip V's by marriage, had crossed the border to attack Pergamene territory.

[40] In 205 BC, following the Peace of Phoenice, Rome turned to Attalus, as its only friend in Asia, for help concerning a religious matter.

A consultation of the Sibylline Books found verses saying that if a foreigner were to make war on Italy, he could be defeated if the Mater Deum Magna Idaea, the Great Mother Goddess, was brought to Rome.

[42] A Roman delegation, led by M. Valerius Laevinus, was dispatched to Pergamon to seek Attalus' aid in gaining an appropriate artifact to bring to Rome.

According to Livy, Attalus received the delegation warmly, and "handed over to them the sacred stone which the natives declared to be 'the Mother of the Gods', and bade them carry it to Rome.

[44] Prevented by the treaty of Phoenice from expansion in the west, Philip V of Macedon set out to extend his power in the Aegean and in Asia Minor.

[48] The same year, Philip invaded Pergamon; although unable to take the defended city, in part due to precautions taken by Attalus to provide for additional fortifications, he demolished the surrounding temples and altars.

Acarnanians with Macedonian support invaded Attica, causing Athens, which had previously maintained its neutrality, to seek help from the enemies of Philip.

At his entrance into the city by the gate Dipylum the priests and priestesses lined the street on both sides: all the temples were then thrown open; victims were placed ready at all the altars; and the king was requested to offer sacrifice.

[53] Sulpicius Galba, now consul, convinced Rome to declare war on Philip[54] and asked Attalus to meet up with the Roman fleet and again conduct a naval campaign, harassing Macedonian possessions in the Aegean.

[57] In the spring of 198 BC, Attalus returned to Greece with twenty-three quinqueremes joining a fleet of twenty Rhodian decked warships at Andros, to complete the conquest of Euboea begun the previous year.

Meanwhile, the new Roman consul for that year, Titus Quinctius Flamininus, had learned that the Achaean League, allies of Macedon, had had a change in leadership which favored Rome.

Attalus won the support of the Sicyonians after purchasing land sacred to Apollo for them, and they erected a colossal statue of him in their market place.

Meanwhile, the Romans moved their forces to the east of the city to control the approaches to Cenchreae, with the Achaeans held the west of Corinth.

King Antiochus III, seemingly taking advantage of Pergamene distraction with the Macedonian War, attacked while Pergamon's ability to defend itself was weak, threatening holdings in Asia Minor.

[63] At the council Attalus spoke first, reminding the Boeotians of the many things he and his ancestors had done for them, but during his address he stopped talking and collapsed, with one side of his body paralyzed.

[66] Antiochus III had seized large amounts of Pergamene territory for his empire, with important putatively Attalid cities such as Phocaea and Thyatira in Seleucid possession.

[66] However, he had also made the city of Pergamon a great center of art and learning, and earned the respect of the Romans and others; historian Esther Hansen calls Attalus's reign not merely the longest of any Attalid monarch, but also "the most laudable".

A decree of Antiochus IV praises "king Attalus and queen Apollonis ... because of their virtue and goodness, which they preserved for their sons, managing their education in this way wisely and well.

"[71] An inscription at Pergamon represents Apollonis as saying that "she always considered herself blessed and gave thanks to the gods, not for wealth or empire, but because she saw her three sons guarding the eldest and him reigning without fear among those who were armed.