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 consuls were necessarily patricians, the tribunes necessarily plebeians. The former had the ampler power, the latter the more unlimited, for the consul submitted to the prohibition and the judgment of the tribunes, but the tribune did not submit himself to the consul. Thus the tribunician power was a copy of the consular; but it was none the less a contrast to it. The power of the consuls was essentially positive, that of the tribunes essentially negative.
The consuls alone were magistrates of the Roman people, not the tribunes; for the former were elected by the whole burgesses, the latter only by the plebeian association. In token of this the consul appeared in public with the apparel and retinue pertaining to state- officials; the tribunes sat on a stool instead of the "chariot seat," and lacked the official attendants, the purple border, and generally all the insignia of magistracy: even in the senate the tribune had neither presidency nor so much as a seat.
Thus in this remarkable institution absolute prohibition was in the most stern and abrupt fashion opposed to absolute command; the quarrel was settled by legally recognizing and regulating the discord between rich and poor.
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Reference address : https://www.ellopos.net/elpenor/rome/2-02-tribunate-plebs-decemvirate.asp?pg=20