Largely because of the Romans' invention of the , a device which enabled them to grapple and board enemy vessels more easily, the Carthaginians were defeated in large naval battles at Mylae (260 BC) and Sulci (257 BC). Encouraged by these and frustrated at the continuing stalemate in Sicily, the Romans changed their focus to a sea-based strategy and developed a plan to invade the Carthaginian heartland in North Africa and threaten Carthage (close to Tunis). Both sides were determined to establish naval supremacy and invested large amounts of money and manpower in maintaining and increasing the size of their navies.