The senate's ultimate authority derived from the esteem and prestige of the senators. This esteem and prestige was based on both precedent and custom, as well as the caliber and reputation of the senators. The senate passed decrees, which were called senatus consulta. These were officially "advice" from the senate to a magistrate. In practice, however, they were usually followed by the magistrates. The focus of the Roman senate was usually directed towards foreign policy. Though it technically had no official role in the management of military conflict, the senate ultimately was the force that oversaw such affairs. The power of the senate expanded over time as the power of the legislative assemblies declined, and the senate took a greater role in ordinary law-making. Its members were usually appointed by Roman Censors, who ordinarily selected newly elected magistrates for membership in the senate, making the senate a partially elected body. During times of military emergency, such as the civil wars of the 1st century BC, this practice became less prevalent, as the Roman Dictator, Triumvir or the senate itself would select its members.
What was the general source of the Roman senate's authority?
the esteem and prestige of the senators