The Saguntines were at war with the Turbuletæ,[511] allies or subjects of Carthage. In contempt of the treaty of 256, Hannibal laid siege to Saguntum, and took it after a siege of several months. He pretended that, in attacking his own allies, the Saguntines had been the aggressors. The people of Saguntum hastened to implore the succour of Rome. The Senate confined itself to despatching commissioners, some to Hannibal, who gave them no attention, and others to Carthage, where they arrived only when Saguntum had ceased to exist. An immense booty, sent by the conqueror, had silenced the faction opposed to the Barcas, and the people, as well as the soldiers, elevated by success, breathed nothing but war. The Roman ambassadors, sent to require indemnities, and even to demand the head of Hannibal, were ill received, and returned declaring hostilities unavoidable.
Rome prepared for war with her usual firmness and energy. One of the consuls was ordered to pass into Sicily, and thence into Africa; the other to lead an army by sea to Spain, and expel the Carthaginians from that country. But, without waiting the issue of negotiations, Hannibal was in full march to transfer the war into Italy. Sometimes treating with the Celtiberian or Gaulish hordes to obtain a passage through their territory, sometimes intimidating them by his arms, he had reached the banks of the Rhone, when the consul charged with the conquest of Spain, P. Cornelius Scipio, landing at the eastern mouth of that river, learnt that Hannibal had already entered the Alps. He then leaves his army to his brother Cneius, returns promptly to Pisa, places himself at the head of the troops destined to fight the Boii, crosses the Po with them, hoping by this rapid movement to surprise the Carthaginian general at the moment when, fatigued and weakened, he entered the plains of Italy.
The two armies met on the banks of the Tessino (536). Scipio, defeated and wounded, fell back on the colony of Placentia. Rejoined in the neighbourhood of that town by his colleague Tib. Sempronius Longus, he again, on the Trebia, offered battle to the Carthaginians. A brilliant victory placed Hannibal in possession of a great part of Liguria and Cisalpine Gaul, the warlike hordes of which received him with enthusiasm and reinforced his army, reduced, after the passage of the mountains, to less than 30,000 men. Flattered by the reception of the Gauls, the Carthaginian general tried also to gain the Italiots, and, announcing himself as the liberator of oppressed peoples, he took care, after the victory, to set at liberty all the prisoners taken from the allies. He hoped that these liberated captives would become for him useful emissaries. In the spring of 537 he entered Etruria, crossed the marshes of the Val di Chiana, and, drawing the Roman army to the neighbourhood of the Lake Trasimenus, into an unfavourable locality, destroyed it almost totally.