The origins of Rome are clouded by myth and legend. It is said that the village which became Rome was first founded by the brothers Romulus and Remus, twins abandoned in the wilderness and raised by a she-wolf. There are those that say that these twins, when they had reached an age to leave their wolf-mother, gathered around them a company of vagabonds, adventurers, and exiles from the villages of the Latins in the Alban hills. Of course, there also those that say that Romulus and Remus were the sons of the war-god Mars, and that the men who followed them to found Rome were noble warriors and princes of the Latin tribes. In truth, the details are unimportant; what matters is that Rome was established, upon the Seven Hills on the banks of the Tiber, with its first settlement at the crest of the Palatine Hill, and Romulus as its first King.
The Roman state grew as quickly as the city itself under Romulus' mighty leadership. From the Palatine Hill, Rome expanded to encompass all seven; from the banks of the Tiber, Rome expanded out into the valleys of Latium. The Latin clans resisted or did not resist, as suited their interests and mood; it mattered little, as Romulus incorporated those who welcomed him and conquered those who opposed him. The Sabines were no different; they resisted more often, perhaps, but no better, than their Latin neighbors, and were quickly brought under the authority of the King of Rome.
Of course, the first King did not live forever, for all his greatness. Romulus died at an old age, having lived a long life of glorious conquest to expand the realm of the city he had built; he died, likewise, with no heir, his brother having been an unfortunate, if necessary, casualty of the city's tumultuous founding. Rome, then, was left with an empty throne, and it is from this circumstance that the tradition of electoral kingship arose in Rome. The great men of the city -- the mighty warriors, the wise priests, the venerable patriarchs of the founding families -- gathered together upon the Capitoline Hill, in the days following the death of their King, and together covenanted to select from amongst their own ranks a new King, to lead Rome to greater glory. They elected as Rome's second King a wise old Latin, who had been among the first settlers to follow Romulus, and who had fought with him against the hill clans and Sabine tribes. It is a testament to the brilliance of the Roman system of government that the first transfer of power in the city's history went off without contest or violence, and an equally strong testament that this second King ruled as well as the first.
Such it was, then, that the tradition of electing a new King upon the death of the old continued down through the generations in Rome. The system was shaped and reshaped, perfected, ritualized. The men of Rome developed for themselves laws of citizenship and suffrage, to regulate who could be King and who could vote for the King. They developed a deliberative body of leading citizens from the old families, to advise the King and maintain the continuity of government. In short, during the reigns of the first few Kings of Rome, they established the framework of the Roman state that would last through the ages.