According to Polybius, after Scipio’s surprise attack and capture of Carthago Nova, the three Carthaginian armies in Iberia remained separated, and their generals at odds with each other, thus giving the Romans a chance to deal with them one by one. Early in 208 BC, Scipio, with 30,000 Roman and Italian troops and 10,000 Spanish auxiliaries, moved against Hasdrubal Barca, whose 30,000-strong force had wintered at Baecula, on the upper reaches of the river Baetis. On learning of the Roman approach, Hasdrubal shifted his camp to a strong defensive position — a high and steep plateau south of Baecula, protected by ravines on the flanks and the river to the front and rear. Moreover, the plateau was formed into two steps, on which Hasdrubal posted his light troops on the lower one and his main camp behind. After his arrival, Scipio was at first uncertain as to how to attack such a formidable position, but concerned that the other two Carthaginian armies might take advantage of his inaction and join with Hasdrubal, he took action on the third day.
Battle
Before his main attack, Scipio sent one detachment to block the entrance to the valley separating the two armies and one to the road leading north to Baecula, thus providing security to his main force, while harassing any Carthaginian attempt to retreat. After these preliminary deployments were done, the Roman light troops advanced against their Carthaginian counterparts on the first step. Despite the steep slope, and under a shower of missile attack, the Romans had little difficulty driving back the Carthaginian light troops once they got into hand-to-hand combat. After reinforcing his leading force, Scipio derived a pincer attack on the flanks of the Carthaginian main camp by ordering Gaius Laelius to lead half of the remaining heavy foot to the right of the enemy position, and he himself scaling the left. Hasdrubal, meanwhile, was under the impression that the Roman attack was only a skirmish and failed to properly deploy his main force, thus his ill-prepared army was caught on three sides by the Romans. Despite being trapped, Hasdrubal was able to retreat unmolested with his elephants, main baggage train, and some of his Carthaginian troops. It appeared that his main losses in the battle were the majority of his light troops and Iberian allies. This was largely due to the legionnaires' choice to plunder the Carthaginian camp rather than pursue Hasdrubal with any earnestness.
Aftermath
After the battle, Hasdrubal led his depleted army over the western passes of the Pyrenees into Gaul, and subsequently into Italy in an attempt to join his brother Hannibal. Scipio's failure to stop Hasdrubal's march to Italy was criticized by the Roman Senate. Scipio did not exploit his victory at Baecula to drive out the Carthaginians from Iberia, instead choosing to withdraw to his base at Tarraco. He secured alliances with many of the Iberian tribes, who switched sides after the Roman successes at Carthago Nova and Baecula. Carthaginian reinforcements landed in Iberia in 207 BC, and would soon launch a final attempt to recover their losses at the Battle of Ilipa in 206 BC.