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
No distinct body of marines was formed, but land troops were employed, when required, for this maritime service. In one instance as many as 120 legionaries fought in each ship on occasion of a great naval battle; in that case however the Roman fleet had at the same time a landing-army on board.
In this way the Romans created a fleet which was a match for the Carthaginians. Those err, who represent this building of a Roman fleet as a fairy tale, and besides they miss their aim; the feat must be understood in order to be admired.
The construction of a fleet by the Romans was in very truth a noble national work--a work through which, by their clear perception of what was needful and possible, by ingenuity in invention, and by energy in resolution and in execution, they rescued their country from a position which was worse than at first it seemed.
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Reference address : https://www.ellopos.net/elpenor/rome/3-02-war-rome-carthage-sicily.asp?pg=23