Whatever may have been the origin of the new king, he was evidently not of the ruling class, the Populus Romanus, and for this reason his sympathies were naturally with the Plebeians, or, as they would now be called, the Commons. The long reign of Servius was marked by the victories of peace, though he was involved in wars with the surrounding nations, in which he was successful. These conquests seemed to fix the king more firmly upon the throne, but they did not render him much less desirous of obtaining the good-will of his subjects, and they never seemed to tempt him to exercise his power in a tyrannical manner. He thought that by marrying his two daughters to two sons of Tarquin, he might make his position on the throne more secure, and he accomplished this intention, but it failed to benefit him as he had expected.

Besides adding largely to the national territory, Servius brought the thirty cities of Latium into a great league with Rome, and built a temple on the Aventine consecrated to Diana (then in high renown at Ephesus), at which the Romans, Latins, and Sabines should worship together in token of their unity as one civil brotherhood, though it was understood that the Romans were chief in rank. On a brazen pillar in this edifice the terms of the treaty on which the league was based were written, and there they remained for centuries. The additions to Roman territory gave Servius an opportunity of strengthening his hold upon the commons, for he took advantage of it to cause a census to be taken under the direction of two Censors, on the basis of which he made new divisions of the people, and new laws by which the plebeians came into greater prominence than they had enjoyed before. The census showed that the city and suburbs contained eighty-three thousand inhabitants.

The increase of population led to the extension of the pomoerium, and Servius completed the city by including within a wall of stone all of the celebrated seven hills [Footnote: The "seven hills" were not always the same. In earlier times they had been: Palatinus, Cermalus, Velia, Fagutal, Oppius, Cispius, and Coelius. Oppius and Cispius, were names of summits of the Esquiline; Velia was a spur of the Palatine; Cermalus and Fagutal, according to Niebuhr, were not hills at all.] - the Palatine, Aventine, Capitoline, Coelian, Quirinal, Viminal, and Esquilian, - for, though new suburbs grew up beyond this wall, the legal limits of the city were not changed until the times of the empire.

The inhabitants within the walls were divided into four "regions" or districts - the Palatine, the Colline, the Esquiline, and the Suburran. The subjected districts outside, which were inhabited by plebeians, were divided into twenty-six other regions, thus forming thirty tribes containing both plebeians and patricians. The census gave Servius a list of all the citizens and their property, and upon the basis of this information he separated the entire population into six classes, comprising one hundred and ninety-three subdivisions or "centuries," thus introducing a new principle, and placing wealth at the bottom of social distinctions, instead of birth. This naturally pleased the plebeians, but was not approved by the citizens of high pedigree, who thus lost some of their prestige. The newly formed centuries together constituted the Comitia Centuriata (gathering of the centuries), or National Assembly, which met for business on the Campus Martius, somewhat after the manner of a New England "Town Meeting." In these conclaves they elected certain magistrates, gave sanction to legislative acts, and decided upon war or peace. This Comitia formed the highest court of appeal known to Roman law.

Besides this general assembly of the entire Populus Romanus, Servius established a Comitia in each tribe, authorized to exercise jurisdiction in local affairs.