Roman senate, governing council of the Roman republic. It was the outgrowth of the council of the kings. By the 3d cent. BC the senate was a group of 300 men with a high degree of political, legislative, and administrative power at Rome. There were serious checks on its power, especially in the hands of the tribunes. The members were chosen by the censors and included theoretically the best citizens; but as it worked out, the senate consisted of ex-magistrates, almost entirely members of a small number of old families from either the patrician or plebeian classes. Membership was usually for life. In the expansion of Rome in the 3d and 2d cent. BC the senate sent out the armies, made the treaties, organized the new domain, and controlled finance. The senatorial conduct of Roman affairs was fairly successful until c.130 BC After that the senate's provincial administration of the huge empire was increasingly inefficient and graft-ridden. However, the authority of the senate was not called into question until the growth of party-class division that developed with the agitation of the Gracchi. The leaders of the senate became also the leaders of the most reactionary group and would yield on no point, economic or political. The fatal development in the republic of two parties, optimates (the senatorial conservatives) and populares, grew out of this resistance to change. The optimates tried to foster the idea that they represented constitutionalism versus subversion, but after Sulla, who combined the bloodiest illegality with the strictest defense of the senate (which he raised to 600 members), such a claim by optimates was hypocritical and cynical. Caesar enlarged the number of the senate to 900. The ruin of the optimates and the senate was accomplished in the proscription of 43 BC after Caesar's assassination. After the proscription what was left of the senate was docile and ineffectual. Augustus lowered the number to 600. As an administrator he found he had to reduce senatorial control in the provinces. Under the principate the senate became a somewhat less hereditary body and gradually came to include provincials from most regions of the empire. It continued to include many of the empire's leading soldiers and administrators, until it lost much influence in the troubles of the 3d cent. AD In the later Roman Empire, it retained some prestige, but very little power. Under Byzantine rule in the 6th cent., the senate disappeared.
See M. Gelzer, The Roman Nobility (1969); R. J. A. Talbert, The Senate of Imperial Rome (1984).