Pyrrhus planned a campaign into Macedonia for the next year with 8,000 infantry and 500 cavalry to which he added Gallic mercenaries.
[1] The expedition originally planned as a limited raid turned into a full-scale invasion when Pyrrhus met with more success than he expected.
Antigonus marched against the invaders and met them in battle in a narrow gorge near the Aous River.
Demoralized by the loss of the elephants, the Macedonians agreed to Pyrrhus' offer to switch sides.
Taking possession of Aegae, the ancient capital of Macedonia, he installed a garrison of Gauls, who greatly offended the Macedonians by digging up the tombs of their kings and leaving the bones scattered about as they searched for gold.