On the other hand the Romans succeeded, by means of a weak corps which advanced along the Lucanian frontier and of the garrison of Venusia, in preventing the Lucanians and Samnites from uniting with Pyrrhus; while the main force--four legions as it would appear, and so, with a corresponding number of allied troops, at least 50,000 strong--marched against Pyrrhus, under the consul Publius Laevinus.
Battle near Heraclea With a view to cover the Tarentine colony of Heraclea, the king had taken up a position with his own and the Tarentine troops between that city and Pandosia (3) (474).

The Romans, covered by their cavalry, forced the passage of the Siris, and opened the battle with a vehement and successful cavalry charge; the king, who led his cavalry in person, was thrown from his horse, and the Greek horsemen, panic-struck by the disappearance of their leader, abandoned the field to the squadrons of the enemy.

Pyrrhus, however, put himself at the head of his infantry, and began a fresh and more decisive engagement.
Seven times the legions and the phalanx met in shock of battle, and still the conflict was undecided.

Then Megacles, one of the best officers of the king, fell, and, because on this hotly-contested day he had worn the king's armour, the army for the second time believed that the king had fallen; the ranks wavered; Laevinus already felt sure of the victory and threw the whole of his cavalry on the flank of the Greeks.

But Pyrrhus, marching with uncovered head through the ranks of the infantry, revived the sinking courage of his troops.
The elephants which had hitherto been kept in reserve were brought up to meet the cavalry; the horses took fright at them; the soldiers, not knowing how to encounter the huge beasts, turned and fled; the masses of disordered horsemen and the pursuing elephants at length broke the compact ranks of the Roman infantry, and the elephants in concert with the excellent Thessalian cavalry wrought great slaughter among the fugitives.