Meanwhile Hannibal hurried up the valley of the Rhone, across the Isara, through the fertile country of the Allobroges, arriving, in sixteen days from Avenio, at the pass of the first Alpine range (Mont du Chat). Crossing this with some difficulty, owing to the nature of the country and the resistance of the Celts, he hastened on through the country of the Centrones, along the north bank of the Isara. As he was leaving this river and approaching the pass of the Little St. Bernard, he was again attacked by the Celts, and obliged to make the ascent amidst continual and bloody encounters. After toiling a day and a night, however, the army reached the summit of the pass. Here, on a table-land, his troops were allowed a brief rest. The hardships of the descent were fully as great, and the fertile valley of the Po was a welcome sight to the half-famished and exhausted soldiers. Here they encamped, in September, and recruited their wearied energies. This famous march of Hannibal from the Rhone lasted thirty-three days, and cost him 20,000 infantry and 3,000 cavalry. The Romans were still unprepared to meet Hannibal. One army was in Spain under Gnaeus Scipio; the other in Sicily, on its way to Africa, under the Consul Sempronius. The only troops immediately available were a few soldiers that had been left in the valley of the Po to restrain the Gauls, who had recently shown signs of defection. Publius Cornelius Scipio, upon his return from Massilia, took command of these. He met Hannibal first in October, 218, near the river Ticinus, a tributary of the Po. A cavalry skirmish followed, in which he was wounded and rescued by his son, a lad of seventeen, afterwards the famous Africanus. The Romans were discomfited, with considerable loss. They then retreated, crossing the Po at Placentia, and destroying the bridge behind them. Hannibal forded the river farther up, and marched along its right bank until he reached its confluence with the Trebia, opposite Placentia. Here he encamped. Meanwhile Sempronius, who had been recalled from Sicily, relieved the disabled Scipio. Early one raw morning in December, 218, the vanguard of the Carthaginians was ordered to cross the Trebia, and, as soon any resistance was met, to retreat. The other troops of Hannibal were drawn up ready to give the enemy a hot reception, if, as he expected, they should pursue his retreating vanguard. Sempronius was caught in the trap, and all his army, except one division of 10,000, was cut to pieces. The survivors took refuge in Placentia and Cremona, where they spent the winter. Sempronius himself escaped to Rome.