This section is from the book "Popular Law Library Vol1 Introduction To The Study Of Law Legal History", by Albert H. Putney. Also see: Popular Law-Dictionary.
The creation of the comitia centuriata and the transference to it of most of the power formerly possessed by the comiatia curiata marked a step away from the old line of demarcation; but as the comitia centuriata was so arranged as to give the weight of power to the richer classes, the practical benefit to the mass of the plebeians was slight.
More important were the reforms of 495-94 B. C. Overawed by the famous secession of the plebeians to the sacred mount, the patricians were compelled to make concessions, and in addition, to redressing some of the existing injustices as to the division of the public lands, consented to the creation of two officers to be elected from and by the plebeians, who were to bear the title of tribunes. The particular duties of the tribunes was the protection of the plebeians, and for this purpose they were given the right to forbid or to "veto" any act of any legislative assembly or any public officer. This was resorted to when there were wrongs of the plebeians to be redressed. Here we have the origin of the "veto power," so familiar to us in our constitution.
By the Publilian Law passed in 471 B. C, a distinctively plebeian assembly was created, called the comitia tributa. This new assembly was composed solely of plebeians who were freeholders, and thus excluded the great majority of freedmen and clients, as well as all the patricians; the clients of patrician families, however, voted in these assemblies, and thus enabled the nobility to exercise no small influence on the result. The Publilian law increased the number of tribunes to five (a little later it was increased to ten), and trans-fered their election to the new comitia tributa. The general legislative power of this assembly was at first small, but it later acquired jurisdiction over all classes of subjects.
One great evil which remained untouched by the reforms already referred to, arose out of the fact that not only was the administration of justice entirely in the hands of the patricians, but the members of this class were also the only persons having any knowledge as to what the law was, and great pains were taken to guard this knowledge from the plebeians. The injustices springing from such an arrangement were so great that in 451 B. C, ten men, known as the decemvirs, were elected to draw up a codification of the Roman Law.