Publius Scipio went to Spain in 544-5, accompanied by the propraetor Marcus Silanus, who was to succeed Nero and to serve as assistant and counsellor to the young commander-in-chief, and by his intimate friend Gaius Laelius as admiral, and furnished with a legion exceeding the usual strength and a well-filled chest. His appearance on the scene was at once signalized by one of the boldest and most fortunate coups de main that are known in history. Of the three Carthaginian generals Hasdrubal Barcas was stationed at the sources, Hasdrubal son of Gisgo at the mouth, of the Tagus, and Mago at the Pillars of Hercules; the nearest of them was ten days' march from the Phoenician capital New Carthage. Suddenly in the spring of 545, before the enemy's armies began to move, Scipio set out with his whole army of nearly 30,000 men and the fleet for this town, which he could reach from the mouth of the Ebro by the coast route in a few days, and surprised the Phoenician garrison, not above 1000 men strong, by a combined attack by sea and land. The town, situated on a tongue of land projecting into the harbour, found itself threatened at once on three sides by the Roman fleet, and on the fourth by the legions; and all help was far distant. Nevertheless the commandant Mago defended himself with resolution and armed the citizens, as the soldiers did not suffice to man the walls. A sortie was attempted; but the Romans repelled it with ease and, without taking time to open a regular siege, began the assault on the landward side. Eagerly the assailants pushed their advance along the narrow land approach to the town; new columns constantly relieved those that were fatigued; the weak garrison was utterly exhausted; but the Romans had gained no advantage. Scipio had not expected any; the assault was merely designed to draw away the garrison from the side next to the harbour, where, having been informed that part of the latter was left dry at ebb-tide, he meditated a second attack. While the assault was raging on the landward side, Scipio sent a division with ladders over the shallow bank "where Neptune himself showed them the way", and they had actually the good fortune to find the walls at that point undefended. Thus the city was won on the first day; whereupon Mago in the citadel capitulated. With the Carthaginian capital there fell into the hands of the Romans 18 dismantled vessels of war and 63 transports, the whole war-stores, considerable supplies of corn, the war-chest of 600 talents (more than; 40,000 pounds), ten thousand captives, among whom were eighteen Carthaginian gerusiasts or judges, and the hostages of all the Spanish allies of Carthage. Scipio promised the hostages permission to return home so soon as their respective communities should have entered into alliance with Rome, and employed the resources which the city afforded to reinforce and improve the condition of his army. He ordered the artisans of New Carthage, 2000 in number, to work for the Roman army, promising to them liberty at the close of the war, and he selected the able-bodied men among the remaining multitude to serve as rowers in the fleet. But the burgesses of the city were spared, and allowed to retain their liberty and former position. Scipio knew the Phoenicians, and was aware that they would obey; and it was important that a city possessing the only excellent harbour on the east coast and rich silver mines should be secured by something more than a garrison.
Success thus crowned the bold enterprise - bold, because it was not unknown to Scipio that Hasdrubal Barcas had received orders from his government to advance towards Gaul and was engaged in fulfilling them, and because the weak division left behind on the Ebro was not in a position seriously to oppose that movement, should the return of Scipio be delayed. But he was again at Tarraco, before Hasdrubal made his appearance on the Ebro. The hazard of the game which the young general played, when he abandoned his primary task in order to execute a dashing stroke, was concealed by the fabulous success which Neptune and Scipio had gained in concert. The marvellous capture of the Phoenician capital so abundantly justified all the expectations which had been formed at home regarding the wondrous youth, that none could venture to utter any adverse opinion. Scipio's command was indefinitely prolonged; he himself resolved no longer to confine his efforts to the meagre task of guarding the passes of the Pyrenees. Already, in consequence of the fall of New Carthage, not only had the Spaniards on the north of the Ebro completely submitted, but even beyond the Ebro the most powerful princes had exchanged the Carthaginian for the Roman protectorate.
Scipio employed the winter of 545-6 in breaking up his fleet and increasing his land army with the men thus acquired, so that he might at once guard the north and assume the offensive in the south more energetically than before; and he marched in 546 to Andalusia. There he: encountered Hasdrubal Barcas, who, in the execution of his long-cherished plan, was moving northward to the help of his brother. A battle took place at Baecula, in which the Romans claimed the victory and professed to have made 10,000 captives; but Hasdrubal substantially attained his end, although at the sacrifice of a portion of his army. With his chest, his elephants, and the best portion of his troops, he fought his way to the north coast of Spain; marching along the shore, he reached the western passes of the Pyrenees which appear to have been unoccupied, and before the bad season began he was in Gaul, where he took up quarters for the winter. It was evident that the resolve of Scipio to combine offensive operations with the defensive which he had been instructed to maintain was inconsiderate and unwise. The immediate task assigned to the Spanish army, which not only Scipio's father and uncle, but even Gaius Marcius and Gaius Nero had accomplished with much inferior means, was not enough for the arrogance of the victorious general at the head of a numerous army; and he was mainly to blame for the extremely critical position of Rome in the summer of 547, when the plan of Hannibal for a combined attack on the Romans was at length realized. But the gods covered the errors of their favourite with laurels. In Italy the peril fortunately passed over; the Romans were glad to accept the bulletin of the ambiguous victory of Baecula, and, when fresh tidings of victory arrived from Spain, they thought no more of the circumstance that they had had to combat the ablest general and the flower of the Hispano-Phoenician army in Italy.
After the removal of Hasdrubal Barcas the two generals who were left in Spain determined for the time being to retire, Hasdrubal son of Gisgo to Lusitania, Mago even to the Baleares; and, until new reinforcements should arrive from Africa, they left the light cavalry of Massinissa alone to wage a desultory warfare in Spain, as Muttines had done so successfully in Sicily. The whole east coast thus fell into the power of the Romans. In the following year (547) Hanno actually made his appearance from Africa with a third army, whereupon Mago and Hasdrubal returned to Andalusia. But Marcus Silanus defeated the united armies of Mago and Hanno, and captured the latter in person. Hasdrubal upon this abandoned the idea of keeping the open field, and distributed his troops among the Andalusian cities, of which Scipio was during this year able to storm only one, Oringis. The Phoenicians seemed vanquished; but yet they were able in the following year (548) once more to send into the field a powerful army, 32 elephants, 4000 horse, and 70,000 foot, far the greater part of whom, it is true, were hastily-collected: Spanish militia. Again a battle took place at Baecula. The Roman army numbered little more than half that of the enemy, and was also to a considerable extent composed of Spaniards. Scipio, like Wellington in similar circumstances, disposed his Spaniards so that they should not partake in the fight - the only possible mode of preventing their dispersion - while on the other hand he threw his Roman troops in the first instance on the Spaniards. The day was nevertheless obstinately contested; but at length the Romans were the victors, and, as a matter of course, the defeat of such an army was equivalent to its complete dissolution - Hasdrubal and Mago singly made their escape to Gades. The Romans were now without a rival in the peninsula; the few towns that did not submit with good will were subdued one by one, and some of them were punished with cruel severity. Scipio was even able to visit Syphax on the African coast, and to enter into communications with him and also with Massinissa with reference to an expedition to Africa - a foolhardy venture, which was not warranted by any corresponding advantage, however much the report of it might please the curiosity of the citizens of the capital at home. Gades alone, where Mago held command, was still Phoenician. For a moment it seemed as if, after the Romans had entered upon the Carthaginian heritage and had sufficiently undeceived the expectation cherished here and there among the Spaniards that after the close of the Phoenician rule they would get rid of their Roman guests also and regain their ancient freedom, a general insurrection against the Romans would break forth in Spain, in which the former allies of Rome would take the lead.