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
The reason for Hannibal's preference of the land route to that by sea is less obvious; for that neither the maritime supremacy of the Romans nor their league with Massilia could have prevented a landing at Genoa, is evident, and was shown by the sequel. Our authorities fail to furnish us with several of the elements, on which a satisfactory answer to this question would depend, and which cannot be supplied by conjecture.
Hannibal had to choose between two evils. Instead of exposing himself to the unknown and less calculable contingencies of a sea voyage and of naval war, it must have seemed to him the better course to accept the assurances, which beyond doubt were seriously meant, of the Boii and Insubres, and the more so that, even if the army should land at Genoa, it would still have mountains to cross; he could hardly know exactly, how much smaller are the difficulties presented by the Apennines at Genoa than by the main chain of the Alps.
At any rate the route which he took was the primitive Celtic route, by which many much larger hordes had crossed the Alps: the ally and deliverer of the Celtic nation might without temerity venture to traverse it.
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Reference address : https://www.ellopos.net/elpenor/rome/3-04-hamilcar-hannibal.asp?pg=33