Titus Livius (Livy), The History of Rome, Book 1
Rev. Canon Roberts, Ed.

43. Those¹ whose property amounted to, or exceeded 100,000 lbs. weight of copper were formed into eighty centuries, forty of juniors and forty of seniors.² [2] These were called the First Class. The seniors were to defend the City, the juniors to serve in the field. The armour which they were to provide themselves with comprised helmet, round shield, greaves, and coat of mail, all of brass; these were to protect the person. Their offensive weapons were spear and sword. [3] To this class were joined two centuries of carpenters whose duty it was to work the engines of war; they were without arms. The Second Class consisted of those whose property amounted to between 75,000 and 100,000 lbs. [4] weight of copper; they were formed, seniors and juniors together, into twenty centuries. Their regulation arms were the same as those of the First Class, except that they had an oblong wooden shield instead of the round brazen one and no coat of mail. [5] The Third Class he formed of those whose property fell as low as 50,000 lbs.; these also consisted of twenty centuries, similarly divided into seniors and juniors. The only difference in the armour was that they did not wear greaves. [6] In the Fourth Class were those whose property did not fall below 25,000 lbs. [7] They also formed twenty centuries; their only arms were a spear and a javelin. The Fifth Class was larger, it formed thirty centuries. They carried slings and stones, and they included the supernumeraries, the horn-blowers, and the trumpeters, who formed three centuries. This Fifth Class was assessed at 11,000 lbs. [8] The rest of the population whose property fell below this were formed into one century and were exempt from military service.

After thus regulating the equipment and distribution of the infantry, he rearranged the cavalry. He enrolled from amongst the principal men of the State twelve centuries. [9] In the same way he made six other centuries (though only three had been formed by Romulus) under the same names under which the first had been inaugurated. For the purchase of the horse, 10,000 lbs. were assigned them from the public treasury; whilst for its keep certain widows were assessed to pay 2000 lbs. each, annually. The burden of all these expenses was shifted from the poor on to the rich.

[10] Then additional privileges were conferred. The former kings had maintained the constitution as handed down by Romulus, viz., manhood suffrage in which all alike possessed the same weight and enjoyed the same rights. Servius introduced a graduation; so that whilst no one was ostensibly deprived of his vote, all the voting power was in the hands of the principal men of the State. [11] The knights were first summoned to record their vote, then the eighty centuries of the infantry of the First Class; if their votes were divided, which seldom happened, it was arranged for the Second Class to be summoned; very seldom did the voting extend to the lowest Class. [12] Nor need it occasion any surprise, that the arrangement which now exists since the completion of the thirty-five tribes, their number being doubled by the centuries of juniors and seniors, does not agree with the total as instituted by Servius Tullius. [13] For, after dividing the City with its districts and the hills which were inhabited into four parts, he called these divisions ‘tribes,’ I think from the tribute they paid, for he also introduced the practice of collecting it at an equal rate according to the assessment. These tribes had nothing to do with the distribution and number of the centuries.