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
The collegiate principle, from which the third and subsequently most current name of the annual kings was derived, assumed in their case an altogether peculiar form. The supreme power was not entrusted to the two magistrates conjointly, but each consul possessed and exercised it for himself as fully and wholly as it had been possessed and exercised by the king.
This was carried so far that, instead of one of the two colleagues undertaking perhaps the administration of justice, and the other the command of the army, they both administered justice simultaneously in the city just as they both set out together to the army; in case of collision the matter was decided by a rotation measured by months or days.
A certain partition of functions withal, at least in the supreme military command, might doubtless take place from the outset--the one consul for example taking the field against the Aequi, and the other against the Volsci--but it had in no wise binding force, and each of the colleagues was legally at liberty to interfere at any time in the province of the other.
When, therefore, supreme power confronted supreme power and the one colleague forbade what the other enjoined, the consular commands neutralized each other. This peculiarly Latin, if not peculiarly Roman, institution of co-ordinate supreme authorities--which in the Roman commonwealth on the whole approved itself as practicable, but to which it will be difficult to find a parallel in any other considerable state --manifestly sprang out of the endeavour to retain the regal power in legally undiminished fulness.
They were thus led not to break up the royal office into parts or to transfer it from an individual to a college, but simply to double it and thereby, if necessary, to neutralize it through its own action.
Do you see any typos or other mistakes? Please let us know and correct them
Reference address : https://www.ellopos.net/elpenor/rome/2-01-constitution-magistrate.asp?pg=8