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
With this co-ordinate jurisdiction there was further associated a co-ordinate initiative in legislation. The right of assembling the members and of procuring decrees on their part already pertained to the tribunes, in so far as no association at all can be conceived without such a right. But it was conferred upon them, in a marked way, by legally securing that the autonomous right of the plebs to assemble and pass resolutions should not be interfered with on the part of the magistrates of the community or, in fact, of the community itself.
At all events it was the necessary preliminary to the legal recognition of the plebs generally, that the tribunes could not be hindered from having their successors elected by the assembly of the plebs and from procuring the confirmation of their criminal sentences by the same body; and this right accordingly was further specially guaranteed to them by the Icilian law (262), which threatened with severe punishment any one who should interrupt the tribune while speaking, or should bid the assembly disperse.
It is evident that under such circumstances the tribune could not well be prevented from taking a vote on other proposals than the choice of his successor and the confirmation of his sentences. Such "resolves of the multitude" (-plebi scita-) were not indeed strictly valid decrees of the people; on the contrary, they were at first little more than are the resolutions of our modern public meetings; but, as the distinction between the comitia of the people and the councils of the multitude was of a formal nature rather than aught else, the validity of these resolves as autonomous determinations of the community was at once claimed at least on the part of the plebeians, and the Icilian law for instance was immediately carried in this way.
Thus was the tribune of the people appointed as a shield and protection for the individual, and as leader and manager for all, provided with unlimited judicial power in criminal proceedings, that in this way he might give emphasis to his command, and lastly even pronounced to be in his person inviolable (-sacrosanctus-), inasmuch as whoever laid hands upon him or his servant was not merely regarded as incurring the vengeance of the gods, but was also among men accounted as if, after legally proven crime, deserving of death.
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Reference address : https://www.ellopos.net/elpenor/rome/2-02-tribunate-plebs-decemvirate.asp?pg=17