At the time of his starting, the Carthaginian power in Spain was secured from Cadiz to the river Ebro. The region between this river and the Pyrenees was inhabited by tribes friendly to the Romans, but unable, in the absence of the latter, to oppose a successful resistance to Hannibal. He put them down, leaving eleven thousand soldiers under Hanno to keep military possession of the country, lest the Romans should establish themselves there, and thus disturb his communications with his base. Cnæus Scipio, however, arrived on the spot by sea the same year with twenty thousand men, defeated Hanno, and occupied both the coast and interior north of the Ebro. The Romans thus held ground by which they entirely closed the road between Hannibal and reinforcements from Hasdrubal, and whence they could attack the Carthaginian power in Spain; while their own communications with Italy, being by water, were secured by their naval supremacy. They made a naval base at Tarragona, confronting that of Hasdrubal at Cartagena, and then invaded the Carthaginian dominions. The war in Spain went on under the elder Scipios, seemingly a side issue, with varying fortune for seven years; at the end of which time Hasdrubal inflicted upon them a crushing defeat, the two brothers were killed, and the Carthaginians nearly succeeded in breaking through to the Pyrenees with reinforcements for Hannibal. The attempt, however, was checked for the moment; and before it could be renewed, the fall of Capua released twelve thousand veteran Romans, who were sent to Spain under Claudius Nero, a man of exceptional ability, to whom was due later the most decisive military movement made by any Roman general during the Second Punic War. This seasonable reinforcement, which again assured the shaken grip on Hasdrubal's line of march, came by sea,--a way which, though most rapid and easy, was closed to the Carthaginians by the Roman navy. Two years later the younger Publius Scipio, celebrated afterward as Africanus, received the command in Spain, and captured Cartagena by a combined military and naval attack; after which he took the most extraordinary step of breaking up his fleet and transferring the seamen to the army. Not contented to act merely as the "containing"[6] force against Hasdrubal by closing the passes of the Pyrenees, Scipio pushed forward into southern Spain, and fought a severe but indecisive battle on the Guadalquivir; after which Hasdrubal slipped away from him, hurried north, crossed the Pyrenees at their extreme west, and pressed on to Italy, where Hannibal's position was daily growing weaker, the natural waste of his army not being replaced.