Beginning in 280 BC, Pyrrhus embarked on a campaign in Magna Graecia (i.e. southern Italy) against the Roman Republic known as the Pyrrhic War, followed by his invasion of Sicily. Ptolemy Keraunos had secured his position on the Macedonian throne by gifting Pyrrhus five-thousand soldiers and twenty war elephants for this endeavor. Pyrrhus returned to Epirus in 275 BC after the stalemate and ultimate failure of both campaigns, which contributed to the rise of Rome now that Greek cities in southern Italy such as Tarentum became Roman allies. Despite having a depleted treasury, Pyrrhus decided to invade Macedonia in 274 BC, due to the perceived political instability of Antigonus II's regime. After defeating the largely mercenary army of Antigonus II at the 274 BC Battle of Aous, Pyrrhus was able to drive him out of Macedonia and force him to take refuge with his naval fleet.