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
These were here for the first time designated as eligible, though only for an extraordinary office. This was a great step in the progress towards full political equality; and it was not too dearly purchased, when the tribunate of the people as well as the right of appeal were suspended while the decemvirate lasted, and the decemvirs were simply bound not to infringe the sworn liberties of the community.
Previously however an embassy was sent to Greece to bring home the laws of Solon and other Greek laws; and it was only on its return that the decemvirs were chosen for the year 303. Although they were at liberty to elect plebeians, the choice fell on patricians alone--so powerful was the nobility still--and it was only when a second election became necessary for 304, that some plebeians were chosen--the first non-patrician magistrates that the Roman community had.
Taking a connected view of these measures, we can scarcely attribute to them any other design than that of substituting for tribunician intercession a limitation of the consular powers by written law. On both sides there must have been a conviction that things could not remain as they were, and the perpetuation of anarchy, while it ruined the commonwealth, was in reality of no benefit to any one.
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Reference address : https://www.ellopos.net/elpenor/rome/2-02-tribunate-plebs-decemvirate.asp?pg=30