Please note that Mommsen uses the AUC chronology (Ab Urbe Condita), i.e. from the founding of the City of Rome. You can use this reference table to have the B.C. dates
From: The History of Rome, by Theodor Mommsen
Translated with the sanction of the author by William Purdie Dickson
Hannibal's Passage of the Alps
Hannibal, who after the passage of the Rhone had in a great assembly of the army explained to his troops the object of his expedition, and had brought forward the Celtic chief Magilus himself, who had arrived from the valley of the Po, to address the army through an interpreter, meanwhile continued his march to the passes of the Alps without obstruction.
Which of these passes he should choose, could not be at once determined either by the shortness of the route or by the disposition of the inhabitants, although he had no time to lose either in circuitous routes or in combat. He had necessarily to select a route which should be practicable for his baggage, his numerous cavalry, and his elephants, and in which an army could procure sufficient means of subsistence either by friendship or by force; for, although Hannibal had made preparations to convey provisions after him on beasts of burden, these could only meet for a few days the wants of an army which still, notwithstanding its great losses, amounted to nearly 50,000 men.
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Reference address : https://www.ellopos.net/elpenor/rome/3-04-hamilcar-hannibal.asp?pg=44