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 may not indeed be regarded in the light of legislation pertaining jointly to the burgesses and the senate, somewhat in the same way as to the two chambers in the constitutional state of the present day; the senate was not so much law-maker as law-guardian, and could only cancel a decree when the community seemed to have exceeded its competence--to have violated by its decree existing obligations towards the gods or towards foreign states or organic institutions of the community.
But still it was a matter of the greatest importance that--to take an example--when the Roman king had proposed a declaration of war and the burgesses had converted it into a decree, and when the satisfaction which the foreign community seemed bound to furnish had been demanded in vain, the Roman envoy invoked the gods as witnesses of the wrong and concluded with the words, "But on these matters we shall consult the elders at home how we may obtain our rights;" it was only when the council of elders had declared its consent, that the war now decreed by the burgesses and approved by the senate was formally declared.
Certainly it was neither the design nor the effect of this rule to occasion a constant interference of the senate with the resolutions of the burgesses, and by such guardianship to divest them of their sovereign power; but, as in the event of a vacancy in the supreme office the senate secured the continuance of the constitution, we find it here also as the shield of legal order in opposition even to the supreme power--the community.
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Reference address : https://www.ellopos.net/elpenor/rome/1-05-original-constitution-rome.asp?pg=31