Doson, with his timely support of Aratus…

The Seleucids, weakened by constant wars against the Ptolemies of Egypt and by succession disputes, have now lost much of Anatolia and eastern Iran.

Attalus of Pergamon invades northern Syria in 224 and annexes considerable Seleucid territory.

Seleucus III Ceraunus, the elder son and successor of Seleucus II Callinicus, ruler of the Hellenistic Seleucid kingdom, who had been killed in 225 by a fall from his horse, takes up the task of reconquering Pergamon in Asia Minor from his cousin Attalus I.

Andromachus, dispatched to Pergamon by Seleucus, is decisively defeated by Attalus and captured.

Cleomenes takes Pellene, …

…Phlius, …

…Argos, and other cities, …

…and Aratus, twice defeated by the Spartans and seeing his life's work imperiled by Cleomenes' revolution, is forced to call upon his old enemy, King Antigonus Doson of Macedon, for assistance.

Seleucus III personally leads an army across the Taurus Mountains.

He is assassinated, however, in Phrygia.

After the assassination of Seleucus, his cousin Achaeus, who had accompanied Ceraunus on this expedition against Attalus, revenges his death; and though he might easily have assumed the royal power, he remains faithful to the family of Seleucus.

Antiochus appoints Achaeus to the command of all Asia Minor on the western side of the Taurus mountains.

Achaeus recovers all the districts which Attalus had gained for the Seleucids once more; but being falsely accused by Hermeias of intending to revolt, he does so in self-defense, assumes the title of king, and rules over the whole of Asia on the western side of the Taurus.

Antiochus III, the younger son of Seleucus II Callinicus, had succeeded his brother Seleucus III to the throne of the disorganized kingdom.

He has retained from the previous administration Hermias as chief minister, Achaeus, a cousin and general of Antiochus III, as governor of Asia Minor, and Molon and his brother Alexander as governors of the eastern provinces, Media and Persis.

Antiochus, when Molon rebels and assumes the title of king in 223, abandons a campaign against Egypt for the conquest of southern Syria, on the advice of Hermias, and marches against Molon.

Diodotus II—accused, it is thought, of treason to Hellenism through his alliance with the nomads—loses his throne around 230 or 223 BCE to a usurper, his brother-in-law Euthydemus I, founder of the Greco-Bactrian Euthydemid dynasty (Polybius, 11.34, 2).