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
As the clans resting upon a family basis were the constituent elements of the state, so the form of the body-politic was modelled after the family both generally and in detail. The household was provided by nature herself with a head in the person of the father with whom it originated, and with whom it perished. But in the community of the people, which was designed to be imperishable, there was no natural master; not at least in that of Rome, which was composed of free and equal husbandmen and could not boast of a nobility by the grace of God.
Accordingly one from its own ranks became its "leader" (-rex-) and lord in the household of the Roman community; as indeed at a later period there were to be found in or near to his dwelling the always blazing hearth and the well-barred store-chamber of the community, the Roman Vestas and the Roman Penates--indications of the visible unity of that supreme household which included all Rome. The regal office began at once and by right, when the position had become vacant and the successor had been designated; but the community did not owe full obedience to the king until he had convoked the assembly of freemen capable of bearing arms and had formally challenged its allegiance.
Then he possessed in its entireness that power over the community which belonged to the house-father in his household; and, like him, he ruled for life. He held intercourse with the gods of the community, whom he consulted and appeased (-auspicia publica-), and he nominated all the priests and priestesses. The agreements which he concluded in name of the community with foreigners were binding upon the whole people; although in other instances no member of the community was bound by an agreement with a non-member. His "command" (-imperium-) was all-powerful in peace and in war, on which account "messengers" (-lictores-, from -licere-, to summon) preceded him with axes and rods on all occasions when he appeared officially.
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Reference address : https://www.ellopos.net/elpenor/rome/1-05-original-constitution-rome.asp?pg=10