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
This mass of troops however was only destined in part for the expedition to Italy. Some 20,000 men were sent to Africa, the smaller portion of them proceeding to the capital and the Phoenician territory proper, the majority to the western point of Africa. For the protection of Spain 12,000 infantry, 2500 cavalry, and nearly the half of the elephants were left behind, in addition to the fleet stationed there; the chief command and the government of Spain were entrusted to Hannibal's younger brother Hasdrubal.
The immediate territory of Carthage was comparatively weakly garrisoned, because the capital afforded in case of need sufficient resources; in like manner a moderate number of infantry sufficed for the present in Spain, where new levies could be procured with ease, whereas a comparatively large proportion of the arms specially African--horses and elephants--was retained there.
The chief care was bestowed in securing the communications between Spain and Africa: with that view the fleet remained in Spain, and western Africa was guarded by a very strong body of troops.
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Reference address : https://www.ellopos.net/elpenor/rome/3-04-hamilcar-hannibal.asp?pg=29