The Battle of Ilerda took place in June 49 BC between the forces of Julius Caesar and the Spanish army of Pompey Magnus, led by his legates Lucius Afranius and Marcus Petreius.

Leaving the siege of Massilia to Gaius Trebonius and Decimus Junius Brutus Albinus, Caesar moved to Hispania Citerior to reinforce the three legions he had sent there as an advance guard under his legate Fabius.

The Pompeians, commanded by Lucius Afranius and Marcus Petreius, encamped on a hill south of the city of Ilerda (Catalan Lleida, Spanish Lérida) in north-east Spain on the western side of the river Sicoris (modern Segre).

This, combined with their skirmish-like combat technique, overwhelmed the Caesarian detachment and his troops were forced to give ground, eventually retreating to safety.

But the soldiers of the ninth legion, elated with success, and eager to repair the loss we had sustained, followed the runaways with so much heat that they were drawn into a place of disadvantage, and found themselves directly under the hill where the town stood, whence when they endeavoured to retire, the enemy again facing about, charged vigorously from the higher ground.

The hill was rough, and steep on each side, extending only so far in breadth as was sufficient for drawing up three cohorts; but they could neither be reinforced in flank, nor sustained by the cavalry.

Here they bravely maintained the fight, though with great disadvantage to themselves, as well on account of the narrowness of the place, as because being posted at the foot of the hill, none of the enemy's darts fell in vain.

The fight had now lasted five hours without intermission, when our men, oppressed by the multitude of the enemy, and having spent all their darts, attacked the mountain sword in hand, and overthrowing such as opposed them, obliged the rest to betake themselves to flight.

The pursuit was continued to the very walls of Ilerda, and some out of fear took shelter in the town, which gave our men an opportunity of making good their retreat.

At the same time the cavalry, though posted disadvantageously in a bottom, found means by their valour to gain the summit of the mountain, and riding between both armies, hindered the enemy from harassing our rear.

Caesar lost about seventy men in the first encounter, among whom was Q. Fulginius, first centurion of the Hastati of the fourteenth legion, who had raised himself by his valour to that rank, through all the inferior orders.

This caused Petreius and Afranius to abandon their camp and the city of Ilerda and retreat towards a second republican army under Marcus Terentius Varro.