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
It is true that, when in the Veientine war it became necessary to prolong the term of service of the soldiers and to keep them under arms not--as hitherto at the utmost--only during summer, but also throughout the winter, and when the farmers, foreseeing their utter economic ruin, were on the point of refusing their consent to the declaration of war, the senate resolved on making an important concession. It charged the pay, which hitherto the tribes had defrayed by contribution, on the state-chest, or in other words, on the produce of the indirect revenues and the domains (348).
It was only in the event of the state-chest being at the moment empty that a general contribution (-tributum-) was imposed on account of the pay; and in that case it was considered as a forced loan and was afterwards repaid by the community. The arrangement was equitable and wise; but, as it was not placed upon the essential foundation of turning the domains to proper account for the benefit of the exchequer, there were added to the increased burden of service frequent contributions, which were none the less ruinous to the man of small means that they were officially regarded not as taxes but as advances.
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Reference address : https://www.ellopos.net/elpenor/rome/2-03-equalization-orders-aristocracy.asp?pg=15