When Pyrrhus learned that the Romans had begun crossing the river he led his Macedonian and Thessalian cavalry to attack the Roman cavalry. His infantry, with peltasts and archers and heavy infantry, began their march as well. The Epirote cavalry successfully disrupted the Roman battle formation and then withdrew. Pyrrhus' peltasts, slingers, and archers began to shoot and his sarissa-wielding phalanxes began to attack. The infantry line was near equal to the Romans' in length as, although Pyrrhus had a small advantage in number, the phalanx was by design deeper than the legion.