The object of the Romans in entering into the treaty was to render possible an attack on Tarentum and to cut off Pyrrhus from his own country, neither of which ends could be attained without the co-operation of the Punic fleet; the object of the Carthaginians was to detain the king in Italy, so that they might be able without molestation to carry into effect their designs on Syracuse.( 5) It was accordingly the interest of both powers in the first instance to secure the sea between Italy and Sicily.

A powerful Carthaginian fleet of 120 sail under the admiral Mago proceeded from Ostia, whither Mago seems to have gone to conclude the treaty, to the Sicilian straits.

The Mamertines, who anticipated righteous punishment for their outrage upon the Greek population of Messana in the event of Pyrrhus becoming ruler of Sicily and Italy, attached themselves closely to the Romans and Carthaginians, and secured for them the Sicilian side of the straits.

The allies would willingly have brought Rhegium also on the opposite coast under their power; but Rome could not possibly pardon the Campanian garrison, and an attempt of the combined Romans and Carthaginians to gain the city by force of arms miscarried.

The Carthaginian fleet sailed thence for Syracuse and blockaded the city by sea, while at the same time a strong Phoenician army began the siege by land (476).