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
Fall of the Decemvirs
The end of the decemvirate is involved in much obscurity. It only remained--so runs the story--for the decemvirs to publish the last two tables, and then to give place to the ordinary magistracy. But they delayed to do so: under the pretext that the laws were not yet ready, they themselves prolonged their magistracy after the expiry of their official year--which was so far possible, as under Roman constitutional law the magistracy called in an extraordinary way to the revision of the constitution could not become legally bound by the term set for its ending.
The moderate section of the aristocracy, with the Valerii and Horatii at their head, are said to have attempted in the senate to compel the abdication of the decemvirate; but the head of the decemvirs Appius Claudius, originally a rigid aristocrat, but now changing into a demagogue and a tyrant, gained the ascendancy in the senate, and the people submitted. The levy of two armies was accomplished without opposition, and war was begun against the Volscians as well as against the Sabines.
Thereupon the former tribune of the people, Lucius Siccius Dentatus, the bravest man in Rome, who had fought in a hundred and twenty battles and had forty-five honourable scars to show, was found dead in front of the camp, foully murdered, as it was said, at the instigation of the decemvirs.
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Reference address : https://www.ellopos.net/elpenor/rome/2-02-tribunate-plebs-decemvirate.asp?pg=34