Titus Livius (Livy), The History of Rome, Book 27
Frank Gardner Moore, Professor Emeritus in Columbia University, Ed.

39. At Rome the confusion was increased by the receipt of a letter from Gaul written by Lucius Porcius, the praetor, reporting that Hasdrubal had left his winter quarters and was already crossing the Alps; [2] that eight thousand Ligurians, enrolled and armed, would join him after he had crossed into Italy, unless some one should be sent into Liguria to forestall them by a war; that he would himself advance, so far as he thought safe, with an army that was not strong. [3] This letter constrained the consuls to complete the levy in haste and to leave for their provinces earlier than they had planned, with this intention, that each of them should keep an enemy in his province, and not allow them to come together and combine their armies in one. [4] Of the greatest assistance in that direction was Hannibal's [p. 367]miscalculation. He had believed, indeed, that his brother¹ would come over into Italy that summer; but when he recalled what he had himself endured during five months, in crossing first the Rhone, and then the Alps, in conflicts with men and the nature of the country, he looked forward to a crossing by no means [5??] so easy and so soon accomplished. This accounted for his slowness in leaving winter quarters. [6] But for Hasdrubal everything moved more quickly and more easily than had been expected by himself and others.² For not only did the Arverni,³ and then in turn other Gallic and Alpine tribes, receive him, but they even followed him to war. [7] And not merely was he leading an army through country for the most part made passable by his brother's crossing,⁴ although previously trackless, but, thanks to the opening up of the Alps by twelve years of habitual use,⁵ they were also crossing through tribes now less savagely disposed. [8] For previously, being never seen by strange peoples and unaccustomed themselves to see a stranger in their own land, they were unfriendly to the human race in general. And at first, not knowing whither the Carthaginian was bound, they had believed that their own rocks and fastnesses and booty in cattle and men were the objects of attack. [9] Then reports of the Punic war, with which Italy had been aflame for eleven years, had made it quite plain to them that the Alps were [p. 369]merely a route; that two very powerful cities,⁶ separated from each other by a wide expanse of sea and land, were contending for empire and supremacy.

These were the reasons which had opened the Alps for Hasdrubal. [10] But what had been gained by the rapidity [11??] of his march he lost by delaying before Placentia, in a futile blockade rather than a siege. [12] He had believed that the storming of a town in the plain was easy, and the reputation of the colony had led him on, thinking that by the destruction of that city he would inspire great alarm in the others. [13] Not only did he hinder himself by that siege, but he had kept back Hannibal, who was just preparing to leave winter quarters, on hearing so much sooner than he had expected news of his brother's crossing. [14] For Hannibal recalled not only how slow was the besieging of cities, but also how vainly he had himself attempted to take that same colony, upon returning as a victor from the Trebia.⁷