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 power of the tribunes, therefore, primarily involved the right of putting a stop to administration and to judicial action at their pleasure, of enabling a person bound to military service to withhold himself from the levy with impunity, of preventing or cancelling the raising of an action and legal execution against the debtor, the initiation of a criminal process and the arrest of the accused while the investigation was pending, and other powers of the same sort.
That this legal help might not be frustrated by the absence of the helpers, it was further ordained that the tribune should not spend a night out of the city, and that his door must stand open day and night. Moreover, it lay in the power of the tribunate of the people through a single word of a single tribune to restrain the adoption of a resolution by the community, which otherwise by virtue of its sovereign right might have without ceremony recalled the privileges conferred by it on the plebs.
But these rights would have been ineffective, if there had not belonged to the tribune of the people an instantaneously operative and irresistible power of enforcing them against him who did not regard them, and especially against the magistrate contravening them. This was conferred in such a form that the acting in opposition to the tribune when making use of his right, above all things the laying hands on his person, which at the Sacred Mount every plebeian, man by man for himself and his descendants, had sworn to protect now and in all time to come from all harm, should be a capital crime; and the exercise of this criminal justice was committed not to the magistrates of the community but to those of the plebs.
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Reference address : https://www.ellopos.net/elpenor/rome/2-02-tribunate-plebs-decemvirate.asp?pg=13