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
This is all that can be looked upon as historically certain in reference to this important event.(2)
2. The well-known fable for the most part refutes itself. To a considerable extent it has been concocted for the explanation of surnames (-Brutus-, -Poplicola-, -Scaevola-). But even its apparently historical ingredients are found on closer examination to have been invented. Of this character is the statement that Brutus was captain of the horsemen (-tribunus celerum-) and in that capacity proposed the decree of the people as to the banishment of the Tarquins; for, according to the Roman constitution, it is quite impossible that a mere officer should have had the right to convoke the curies.
The whole of this statement has evidently been invented with the view of furnishing a legal basis for the Roman republic; and very ill invented it is, for in its case the -tribunus celerum- is confounded with the entirely different -magister equitum- (Cf. I. V. Burdens Of The Burgesses f.), and then the right of convoking the centuries which pertained to the latter by virtue of his praetorian rank is made to apply to the assembly of the curies.
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Reference address : https://www.ellopos.net/elpenor/rome/2-01-constitution-magistrate.asp?pg=5