Polybius: the First Punic War
Polybius' World History was translated by W.R. Paton.
Polybius; cast from a lost monument in Cleitor (Greece) (Museo nazionale della civiltà romana, Rome)
Book 1, chapter 9
For observing that the Syracusans, every time they dispatch their forces on an expedition accompanied by their supreme magistrates, begin quarreling among themselves and introducing continual changes, and knowing that Leptines had a wider circle of dependents and enjoyed more credit than any other burgher and had an especially high name among the common people, he allied himself with him by marriage, so that whenever he had to take the field himself he might leave him behind as a sort of reserve force. He married, then, the daughter of this Leptines, and finding that the veteran mercenaries were disaffected and turbulent, he marched out in force professedly against the foreigners who had occupied Messana.He met the enemy near Centuripa and offered battle near the river Cyamosorus. He held back the citizen cavalry and infantry at a distance under his personal command as if he meant to attack on another side, but advancing the mercenaries he allowed them all to be cut up by the Campanians. During their rout he himself retired safely to Syracuse with the citizens.
Having thus efficiently accompanied his purpose and purged the army of its turbulent and seditious element, he himself enlisted a considerable number of mercenaries and henceforth continued to rule in safety.
[265 BCE] Observing that the Mamertines, owing to their success, were behaving in a bold and reckless manner, he efficiently armed and trained the urban levies and leading them out engaged the enemy in the Mylaean plain near the river Longanus, and inflicted a severe defeat on them, capturing their leaders. This put an end to the audacity of the Mamertines, and on his return to Syracuse he was with one voice proclaimed king by all the allies.