+67.+ But the Celtic contingent of the Roman army, seeing that Hannibal’s prospects looked the brighter of the two, concerted their plans for a fixed time, and waited in their several tents for the moment of carrying them out. When the men within the rampart of the camp had taken their supper and were gone to bed, the Celts let more than half the night pass, and just about the time of the morning watch armed themselves and fell upon the Romans who were quartered nearest to them; killed a considerable number, and wounded not a few; and, finally, cutting off the heads of the slain, departed with them to join the Carthaginians, to the number of two thousand infantry and nearly two hundred cavalry. They were received with great satisfaction by Hannibal; who, after addressing them encouragingly, and promising them all suitable rewards, sent them to their several cities, to declare to their compatriots what they had done, and to urge them to make alliance with him: for he knew that they would now all feel compelled to take part with him, when they learnt the treachery of which their fellow-countrymen had been guilty to the Romans. Just at the same time the Boii came in, and handed over to him the three Agrarian Commissioners, sent from Rome to divide the lands; whom, as I have already related, they had seized by a sudden act of treachery at the beginning of the war. Hannibal gratefully acknowledged their good intention, and made a formal alliance with those who came: but he handed them back their prisoners, bidding them keep them safe, in order to get back their own hostages from Rome, as they intended at first. [Sidenote: Scipio changes his position at Placentia to one on the Trebia.] Publius regarded this treachery as of most serious importance; and feeling sure that the Celts in the neighbourhood had long been ill-disposed, and would, after this event, all incline to the Carthaginians, he made up his mind that some precaution for the future was necessary. The next night, therefore, just before the morning watch, he broke up his camp and marched for the river Trebia, and the high ground near it, feeling confidence in the protection which the strength of the position and the neighbourhood of his allies would give him. [Sidenote: Hannibal follows him.] +68.+ When Hannibal was informed of Scipio’s change of quarters, he sent the Numidian horse in pursuit at once, and the rest soon afterwards, following close behind with his main army. The Numidians, finding the Roman camp empty, stopped to set fire to it: which proved of great service to the Romans; for if they had pushed on and caught up the Roman baggage, a large number of the rear-guard would have certainly been killed by the cavalry in the open plains. But as it was, the greater part of them got across the River Trebia in time; while those who were after all too far in the rear to escape, were either killed or made prisoners by the Carthaginians.