The first king was deified as Quirinus after his death. It was said that Mars had taken him to turn him into a god. Romulus was succeeded by the Sabine Numa Pompilius, who stood out for his religious piousness, establishing the state religion and founding the temple of Janus (the god of the two faces). So much so that he is known as the priest-king.

The third king was Tullus Hostilius, who stood out for his military glory, a warrior character and desire for expansion. He unleashed a civil war with Alba Longa and also fought against the powerful Etruscan city of Veii and against the Sabines. To his reign corresponds the mythical confrontation between the three twins Horatii and the three Curiatii to decide the fate of the civil war without bloodshed between brother peoples; this confrontation ended with a Roman victory and with the settlement of the Albans on Caelian Hill.

Tullus Hostilius was succeeded by Ancus Marcius, who stood out for reconciling his religious duties with those of monarch, and enlarged Rome with the addition of the Aventine and Janiculum Hills. To his reign also corresponds the first great engineering work of his people: the Pons Sublicius, a bridge of stakes on the Tiber River, whose guardian, the Pontifex Maximus, ended up acquiring priestly functions and became leader of the Collegium Pontificum or College of Pontiffs and main authority in religious matters.

These first four kings are considered agrarian, for representing a type of archaic society based on the resources that they themselves could procure. Even so, we find in this period the origin of insтιтutions and mechanisms of organization that would be fundamental in the rest of Roman history.