The comitia centuriata was originally an assembly of the Roman citizens in the form of an army, and the divisions into classes was based upon the kind of equipment with which each soldier was able to provide himself. The eighteen centuries of knights represented the cavalry of the army. These centuries of knights possessed the right of having their votes taken first, which constituted another advantage for the wealthy classes. In 241 B.C. the knights were deprived of their right of voting first, but this privilege was given to the centuries of the first rank, assigned by lot.
The comitia tributa, or assembly of the tribes, first met in 489 B.C., it being convened by the Senate at that time to sit in judgment upon a patrician, Coriolanus, the responsibility for whose fate the Senate desired to throw upon the plebeians. This assembly was originally a strictly plebeian body, and its original authority was limited to the administration of the business of the plebeian order. The class character of the comitia tributa is indicated by its original name--_concilium tributum plebis_, the word _concilium_ indicating a conference of a certain part of the people rather than a legislative assembly of the whole people.
It would be hard to say whether it was the increased power of the tribunes which developed the authority of the comitia tributa, or whether it was the increased power of the comitia tributa which first gave to the tribunes the vast power which they were ultimately able to exercise in Rome. However this may be, the fact is evident that the power of the comitia tributa and of the tribunes rose together. At a later date, membership in the comitia tributa was not limited to the plebeians, but the influence of the patricians in this assembly was always inconsiderable and they generally absented themselves from its meetings. Although the wealthy classes had no predominating influence in the comitia tributa, its decision upon any question was far from being, necessarily, the decision of the majority. Measures submitted to the comitia tributa were carried or defeated by the vote of the majority of the tribes, and the numbers enrolled in each tribe were very unequal, all the inhabitants of the city of Rome being enrolled into four tribes, and a very disproportionate power being thus given to the rural voters.