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
Gaius Gracchus had by entrusting the posts of jurymen to men of equestrian census procured for the capitalist class an indirect share in administering and in governing, which proved itself not seldom stronger than the official adminis-tration and government; Sulla abolished the equestrian and restored the senatorial courts. Gaius Gracchus or at any rate the Gracchan period had conceded to the equites a special place at the popular festivals, such as the senators had for long possessed;(10) Sulla abolished it and relegated the equites to the plebeian benches.(11)
10. Cf. III. XI. Separation of the Orders in the Theatre
11. Cf. IV. III. Insignia of the Equites. Tradition has not indeed informed us by whom that law was issued, which rendered it necessary that the earlier privilege should be renewed by the Roscian theatre-law of 687 (Becker-Friedlander, iv, 531); but under the circumstances the author of that law was undoubtedly Sulla.
The equestrian order, created as such by Gaius Gracchus, was deprived of its political existence by Sulla. The senate was to exercise the supreme power in legislation, administration, and jurisdiction, unconditionally, indivisibly, and permanently, and was to be distinguished also by outward tokens not merely as a privileged, but as the only privileged, order.
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Reference address : https://www.ellopos.net/elpenor/rome/4-10-sullan-constitution.asp?pg=20