Yet after a few days’ rest Hannibal went straight for the nearest Roman force. This force was now on the north bank of the Po under Scipio, who had returned from the Rhone to Italy. Pushing it back to the new colony of Placentia, where it was joined by that of the other consul Sempronius, Hannibal utterly defeated the combined Roman armies on the little river Trebbia which runs down to that city (now Piacenza) from the Apennines. The Roman power in the plain of the Po was instantly paralysed by this defeat, and the victor at once set himself to organise alliances with the Gallic tribes while he rested and recruited his weary troops. But from the Gauls he got no substantial help; that fickle people had no great reason to welcome an invader when once he was in their territory. And perhaps this was fortunate for him; for if he had marched into central Italy as leader of a Gallic army he would have strengthened, not weakened, the resistance of the whole Italian federation that Rome had so solidly organised. His knowledge of the motives which held this federation together must surely have been seriously imperfect. But in the spring he crossed the Apennines, and made his way through the marshy and malarious district around the lower Arno, where it is said he lost an eye from ophthalmia, to meet the consul Flaminius, who had been sent to cover the approach to Rome with a large army. Slipping past Flaminius, Hannibal concealed his army among the hills and woods on the eastern shore of the lake of Trasimene, along the western bank of which the railway now runs on its way from Florence to Rome; and here he lay in wait for his prey. Flaminius walked into the trap laid for him; his army was totally destroyed, and he himself was killed. There was now nothing to stop the conqueror if he chose to march straight on Rome.