Alexander the Great deployed catapults against the Scythians at the battle of the Jaxartes River.
The Scythians and Macedonians were positioned on either side of the Jaxartes River. The river was wide enough that neither could shoot the other with bows. To cross the river Alexander had his men put together enough makeshift rafts so they could all cross at once, then he positioned his catapults along the river. The Catapults could reach the far side of the river & cleared the Scythians away from the bank and gave room for the Macedonian army to land.

With chosen attendants, the king, was the first to unmoor his raft. He ordered a movement to the opposite bank. The Scythian advanced lines of horse stood at the water's edge, to prevent the rafts from being laid on the beach. Besides an army in array guarding the bank, a serious consternation assailed the floating forces; for the steersmen could not direct the course of the rafts, impelled obliquely by the stream, and the soldiers, staggering, apprehensive that they should be shaken off, disturbed the rowers. Nor could they launch their javelins with a spring, more solicitous to stand securely, than to annoy the enemy. They were preserved by their military engines, bolts from which were shot with effect upon the Barbarians, crowded together, and rashly exposing themselves. On their part, the Barbarians discharged clouds of arrows on the rafts; so that there was scarcely a shield pierced with multiplied barbs. At length the rafts begin to lean on the shore; when the front men, with shields, rising together, cast their javelins with a more certain aim and a freer spring. The Scythian horse treading backward in terror, the Macedonians, encouraging each other, leap with alacrity on land; and press, with a quick step, upon the confused enemy. Such troops of horsemen, then, as had their chargers bridled, broke the Barbarian line. Meanwhile, the rest of the army, covered by those who were engaged, prepared for action.
Quintus Curtius Rufus - The Life and Reign of Alexander the Great - Chap. VIII