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
As to the Management of Finances
The financial system of the Roman community also retrograded rather than advanced during this epoch. The amount of their revenues, indeed, was visibly on the increase. The indirect taxes--there were no direct taxes in Rome--increased in consequence of the enlargement of the Roman territory, which rendered it necessary, for example, to institute new customs-offices along the Campanian and Bruttian coasts at Puteoli, Castra (Squillace), and elsewhere, in 555 and 575.
The same reason led to the new salt-tariff of 550 fixing the scale of prices at which salt was to be sold in the different districts of Italy, as it was no longer possible to furnish salt at one and the same price to the Roman burgesses now scattered throughout the land; but, as the Roman government probably supplied the burgesses with salt at cost price, if not below it, this financial measure yielded no gain to the state. Still more considerable was the increase in the produce of the domains. The duty indeed, which of right was payable to the treasury from the Italian domain-lands granted for occupation, was in the great majority of cases neither demanded nor paid.
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Reference address : https://www.ellopos.net/elpenor/rome/3-11-government-governed.asp?pg=24