Wikipedia
Mamertines
The Mamertines (Mamertini "sons of Mars") were mercenaries of Italian origin who had been hired from their home in Campania by Agathocles (361 – 289 BCE), Tyrant of Syracuse and self-proclaimed King of Sicily. After Syracuse lost the Third Sicilian War, the city of Messana was ceded to Carthage in 307 BC. When Agathocles died in 289 BC he left many of his mercenaries idle and unemployed in Sicily. Most of them returned home but some liking the climate and the prospect of adventure on a foreign island remained. They played a major role in the lead up to the First Punic War.
In 280 BC, the Syracusans appealed to King Pyrrhus of Epirus for help against the Mamertines.