The siege of Syracuse by Carthago, and the liberation by Pyrrhus (278BC)

 The Carthaginians, having made an alliance with the Romans […] they continued to guard the Strait, watching against any attempt by Pyrrhus to cross […]

While [Pyrrhus] was making ready to set sail, the Carthaginians were besieging Syracuse both by land and by sea; they blockaded the Great Harbour with a hundred ships, and on land they carried on operations close to the walls with 50.000 men. Thus they held the Syracusans pent up while they overran their territory and laid it waste.

Consequently the Syracusans, being exhausted by the war, pinned their hopes on Pyrrhus, he embarked his men, his elephants, and his other equipment of war aboard his ships, set sail from Tarentum, and put in at Locri on the tenth day.

Thence after adding Tyndarion, the dynast of Tauromenia, to his alliance and after obtaining soldiers from him, he sailed to Catana. There, having been welcomed by the inhabitants with great state and crowned with golden crowns, he disembarked his infantry. As they made their way to Syracuse, the fleet accompanied them in battle array.

 When they approached Syracuse, the Carthaginians, who had sent away thirty ships on some necessary missions, did not venture to do battle with the ships that remained. Thus Pyrrhus sailed unchallenged into Syracuse, and accepted delivery of the Island from Thoenon, and of the rest of the city from the citizens and Sosistratus. 

Diodorus Siculus (Library of History, fragment of Book XXII )