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
We can easily understand--especially if we bear in mind that in the battles of that period, where the naked weapon predominated, it was really the hand- to-hand encounter that proved decisive--how a deliberative assembly might direct such operations, and how any one who just was burgomaster might command the troops. All this was changed in a moment. The field of battle stretched away to an incalculable distance, to the unknown regions of another continent, and beyond a broad expanse of sea; every wave was a highway for the enemy; from any harbour he might be expected to issue for his onward march.
The siege of strong places, particularly maritime fortresses, in which the first tacticians of Greece had failed, had now for the first time to be attempted by the Romans. A land army and the system of a civic militia no longer sufficed. It was essential to create a fleet, and, what was more difficult, to employ it; it was essential to find out the true points of attack and defence, to combine and to direct masses, to calculate expeditions extending over long periods and great distances, and to adjust their co-operation; if these things were not attended to, even an enemy far weaker in the tactics of the field might easily vanquish a stronger opponent. Is there any wonder that the reins of government in such an exigency slipped from the hands of a deliberative assembly and of commanding burgomasters?
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Reference address : https://www.ellopos.net/elpenor/rome/3-02-war-rome-carthage-sicily.asp?pg=56