Titus Livius (Livy), The History of Rome, Book 21
Benjamin Oliver Foster, Ph.D., Ed.

56. In their terror they were now on the point of charging their own people, when Hannibal gave orders to drive them from the centre to the extreme left wing, against the Gallic auxiliaries. Here they immediately caused a decided stampede, and the [p. 167]Romans experienced a fresh alarm when they saw B.C. 218 their auxiliaries routed. [2] And so, hemmed in as they now were on every side, about ten thousand men, when they found it impossible to escape at any other point, forced a passage, with great slaughter of their enemies, through the Carthaginian centre, which was composed of Gallic auxiliaries, and being cut off by the river [3??] from returning to their camp and so blinded by the rain that they could not well discern where to help their comrades, took the shortest way to Placentia.¹ After that sundry groups broke out at various points. [4] Those who headed for the river were either drowned in its eddies, or, while they hesitated to enter it, were overtaken by the enemy; [5] but those who scattered over the countryside in flight made their way by following the tracks of the retreating column, to Placentia; others, venturing, in their terror of the enemy, to attempt the river, got across, and reached the camp. [6] The mingled rain and snow and the intolerable sharpness of the cold brought death to many men and beasts of burden and to almost all the elephants.² [7] The Phoenicians pursued their enemies no further than to the river Trebia, and got back to camp so benumbed and chilled as hardly to feel the joy of victory. Consequently, when, in the night that followed, the garrison of the camp, and such soldiers without arms [8??] for the most part-as had survived the rout, were crossing the Trebia on rafts, they either heard nothing, owing to the noise made by the rain, or being unable, for weariness and wounds, to bestir themselves, pretended not to hear; and unmolested Polybius (II. lxxiv, 11), all but one perished from the effects of the rain and snow that followed the battle. [9] [p. 169]by the enemy Scipio led his army in silence to B.C. 218 Placentia, and thence-after crossing the Po-to Cremona, so that that one town might not be overburdened with furnishing winter quarters for two armies.