Soon after the fall of the city Laelius sailed in a quinquereme to carry the news to Rome, Scipio anticipating that this great success should coax more support from the Senate. He remained at New Carthage for some time, subjecting his army to a rigorous training programme, before retiring to winter at Tarraco. The situation in Spain was beginning to change. The loss of New Carthage was a major blow to Carthaginian prestige as well as depriving them of resources and a vital base. Since the Punic victories in 211 their treatment of the Spanish tribes had become harsher, since there was less need to keep them content and prevent defections to Rome. Many leaders responded to the Roman diplomacy, including Indibilis of the Ilergetes who had remained staunchly loyal to the Carthaginians up until this point, in spite of his capture in 218. Scipio seems to have planned to confront one of the main Punic armies in the next campaigning season, drawing men off from the fleet to bolster the strength of his field army. Carthaginian objectives are harder to reconstruct. Hasdrubal Barca was clearly already planning the expedition to Italy which he would in fact lead later in the year. He resolved to seek a decisive encounter with Scipio, although it is hard to credit Polybius' statement that he only definitely planned to move on Italy if he lost the battle.13
When Scipio led his army out of Tarraco in the spring of 208 he found Hasdrubal near Baecula, almost certainly the modern town of Bailen, in an area famous for its silver mines. It was in the same rugged country that Napoleon's army suffered one of its first serious defeats when General Dupont was forced to surrender to a Spanish army in 1808. As soon as he received reports of the Romans' approach, Hasdrubal camped on high ground, his rear protected by a river, and his flanks by rocky hillocks. In front, at the top of the slope, he positioned a strong guard of formed troops to protect the camp. In was a very strong position, one which no general would relish attacking, which makes it a strange choice if Hasdrubal actually wanted to fight a battle. Perhaps he was hoping to keep the Romans occupied until Mago or Hasdrubal Gisgo could arrive to overwhelm them with numbers, or possibly that the fear of this would make the Romans fight in such unfavourable circumstances. For two days Scipio observed the enemy from the valley below, before deciding that he must attack in case the other Punic commanders were approaching.14
Scipio sent some velites supported by formed infantry in battle order straight up the slope to engage the Punic covering force. Attacking with great enthusiasm, the Romans slowly drove the enemy back. Livy even claims that the army's slaves, the calones, joined in the advance, picking up stones from the ground and lobbing them at the enemy. As they approached the more level summit, the willingness of the velites and the formed maniples to close to hand-to-hand combat proved too much for the Punic light troops, persuading Hasdrubal to order out the remainder of his army and begin forming them in a line near the top of the ridge. Scipio had already divided the remainder of his army into two halves, leading one himself and putting Laelius in charge of the other. It was now that the months of training began to prove their value as the two Roman columns marched to outflank the enemy. Scipio led his section of the army to the left, climbing the high ground and reaching the summit where they deployed into a fighting line threatening the enemy flank. Laelius troops performed the same manoeuvre on the right. The Romans had gained the high ground before Hasdrubal had fully formed his army up and there was no time to alter his orders and place some of the troops to face either flank. As the Romans attacked, the Punic army rapidly gave way, Hasdrubal ordering the unengaged troops to withdraw.
Livy claims that 8,000 Carthaginians fell in the pursuit, although Polybius gives figures of 10,000 foot and 2,000 horse for the prisoners. Both he and Polybius state that Hasdrubal began to withdraw very early in, or even before, the fighting, sending away his slow-moving elephants and his treasury. Rallying as many fugitives as possible, he then led them north towards the valley of the Tagus and began his long march to Italy. His actions must raise the question of whether or not he had really wished to fight in the first place. Even if he had, the reverse at Baecula does not seem to have been a serious enough defeat to upset his plans, unlike Ibera in 215. Scipio did not attempt to block Hasdrubal's escape and it seems unlikely that his small army could have done this. Even after Hasdrubal had left the Peninsula Scipio was still outnumbered by the Punic forces there. The victory at Baecula certainly encouraged more Spanish leaders to join the Romans, some of them saluting Scipio as king, a title so alien to the Roman system that he was at pains to stop its use.15
It may be that the scale of Scipio's success at Baecula has been exaggerated by sources favourable to his family. Even so, the battle demonstrated once more his boldness and imaginative tactics. The manipulation to his advantage of the formal manoeuvring before a battle and the ability to wrong-foot the enemy commander were to be a feature of several of his later battles. This was made possible by the tactical flexibility of the legions under his command, the product of long and careful training.