After the death of Seleucus, the empire he left faced many trials, both from internal and external forces. Antiochus I fought off an attack from the Gauls successfully, but could not defeat the King of Pergamon Eumenes I in 262 BCE, guaranteeing Pergamon's independence. Antiochus II named Theos, or "divine", was poisoned by his first wife, who in turn poisoned Berenice Phernophorus, second wife of Antiochus and the daughter of Ptolemy III Euergetes. Antiochus II's son from his first wife, Seleucus II Callinicus, ended up as ruler of the Seleucids after this tragedy. These turn of events made Ptolemy III very angry, and led to the invasion of the empire (the Third Syrian War) in 246 BCE. This invasion leads to victory for Ptolemy III at Antioch and Seleucia, and he grants the lands of Phrygia to Pontus's Mithridates II in 245 BCE as a wedding gift.
