The policy of the kings consisted in blending together the different races and breaking down the barriers which separated the different classes. To effect the first of these objects, they divided the lower class of the people into corporations,[35] and augmented the number of the tribes and changed their constitution;[36] but to effect the second, they introduced, to the great discontent of the higher class, plebeians among the patricians,[37] and raised the freedmen to the rank of citizens.[38] In this manner, each curia became considerably increased in numbers; but, as the votes were taken by head, the poor patricians were numerically stronger than the rich.

Servius Tullius, though he preserved the curiæ, deprived them of their military organisation, that is, he no longer made it the basis of his system of recruiting. He instituted the centuries, with the double aim of giving as a principle the right of suffrage to all the citizens, and of creating an army which was more national, inasmuch as he introduced the plebeians into it; his design was indeed to throw on the richest citizens the burden of war,[39] which was just, each equipping and maintaining himself at his own cost. The citizens were no longer classified by castes, but according to their fortunes. Patricians and plebeians were placed in the same rank if their income was equal. The influence of the rich predominated, without doubt, but only in proportion to the sacrifices required of them.

Servius Tullius ordered a general report of the population to be made, in which every one was obliged to declare his age, his fortune, the name of his tribe and that of his father, and the number of his children and of his slaves. This operation was called census.[40] The report was inscribed on tables,[41] and, once terminated, all the citizens were called together in arms in the Campus Martius. This review was called the closing of the lustrum, because it was accompanied with sacrifices and purifications named lustrations. The term lustrum was applied to the interval of five years between two censuses.[42]

The citizens were divided into six classes,[43] and into a hundred and ninety-three centuries, according to the fortune of each, beginning with the richest and ending with the poorest. The first class comprised ninety-eight centuries, eighteen of which were knights; the second and fourth, twenty-two; the third, twenty; the fifth, thirty; and the sixth, although the most numerous, forming only one.[44] The first class contained a smaller number of citizens, yet, having a greater number of centuries, it was obliged to pay more than half the tax, and furnish more legionaries than any other class.

The votes continued to be taken by head, as in the curiæ, but the majority of the votes in each century counted only for one suffrage. Now, as the first class had ninety-eight centuries, while the others, taken together, had only ninety-five, it is clear that the votes of the first class were enough to carry the majority. The eighteen centuries of knights first gave their votes, and then the eighty centuries of the first class: if they were not agreed, appeal was made to the vote of the second class, and so on in succession; but, says Livy, it hardly ever happened that they were obliged to descend to the last.[45] Though, according to its original signification, the century should represent a hundred men, it already contained a considerably greater number. Each century was divided into the active part, including all the men from eighteen to forty-six years of age, and the sedentary part, charged with the guard of the town, composed of men from forty-six to sixty years old.[46]

With regard to those of the sixth class, omitted altogether by many authors, they were exempt from all military service, or, at any rate, they were enrolled only in case of extreme danger.[47] The centuries of knights, who formed the cavalry, recruited among the richest citizens, tended to introduce a separate order among the nobility,[48] which shows the importance of the chief called to their command. In fact, the chief of the celeres was, after the king, the first magistrate of the city, as, at a later period, under the Republic, the magister equitum became the lieutenant of the dictator.

The first census of Servius Tullius gave a force of eighty thousand men in a condition to bear arms,[49] which is equivalent to two hundred and ninety thousand persons of the two sexes, to whom may be added, from conjectures, which, however, are rather vague, fifteen thousand artisans, merchants, or indigent people, deprived of all rights of citizenship, and fifteen thousand slaves.[50]

The comitia by centuries were charged with the election of the magistrates, but the comitia by curiæ, being the primitive form of the patrician assembly, continued to decree on the most important religious and military affairs, and remained in possession of all which had not been formally given to the centuries. Solon effected, about the same epoch, in Athens, a similar revolution, so that, at the same time, the two most famous towns of the ancient world no longer took birth as the basis of the right of suffrage, but fortune.

Servius Tullius promulgated a great number of laws favourable to the people; he established the principle that the property only of the debtor, and not his person, should be responsible for his debt. He also authorised the plebeians to become the patrons of their freedmen, which allowed the richest of the former to create for themselves a clientèle resembling that of the patricians.[51]