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
The New Military Organization
He held in his hand a formidable weapon in the newly organized army. Previously to his time the fundamental principle of the Servian constitution--by which the levy was limited entirely to the burgesses possessed of property, and the distinctions as to armour were regulated solely by the property qualification(2)--had necessarily been in various respects relaxed.
2. Cf. I. VI. The Servian Constitution, II. III. Its Composition
The minimum census of 11,000 -asses- (43 pounds), which bound its possessor to enter the burgess-army, had been lowered to 4000 (17 pounds;(3)).
3. Cf. III. XI. Reforms in the Military Service
The older six property-classes, distinguished by their respective kinds of armour, had been restricted to three; for, while in accordance with the Servian organization they selected the cavalry from the wealthiest, and the light-armed from the poorest, of those liable to serve, they arranged the middle class, the proper infantry of the line, no longer according to property but according to age of service, in the three divisions of -hastati-, -principes-, and -triarii-.
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Reference address : https://www.ellopos.net/elpenor/rome/4-06-marius-revolution-drusus-reform.asp?pg=7