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 the two--not standing--pronouncers-of-judgment for revolt and high treason (-duoviri perduellionis-) and the two standing trackers of murder, the -quaestores parricidii-. Something similar may perhaps have occurred in the regal period, where the king had himself represented in such processes;(6) but the standing character of the latter institution, and the collegiate principle carried out in both, belong at any rate to the republic.
6. Cf. I. XI. Crimes
The latter arrangement became of great importance also, in so far that thereby for the first time alongside of the two standing supreme magistrates were placed two assistants, whom each supreme magistrate nominated at his entrance on office, and who in due course also went out with him on his leaving it--whose position thus, like the supreme magistracy itself, was organized according to the principles of a standing office, of a collegiate form, and of an annual tenure.
This was not indeed as yet the inferior magistracy itself, at least not in the sense which the republic associated with the magisterial position, inasmuch as the commissioners did not emanate from the choice of the community; but it doubtless became the starting-point for the institution of subordinate magistrates, which was afterwards developed in so manifold ways.
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Reference address : https://www.ellopos.net/elpenor/rome/2-01-constitution-magistrate.asp?pg=13