The Roman Senate (Lat., Senatus) was a deliberative body which was important in the government of both the Roman Republic and the Roman Empire. The word Senatus is derived from the Latin word senex ("old man" or "elder"); literally, "Senate" is understood to mean something along the lines of "council of elders".
Tradition held that the Senate was first established by Romulus and Remus, the mythical founders of Rome, as an advisory council consisting of the 100 patrician heads of families, called Patres ("Fathers"). Later, when plebeian senators were drafted into the body, they were called Conscripti ("Conscripted Men"), because they had no choice but to take their seats. Thus, the members of the Senate were addressed as "Patres et Conscripti", which was gradually run together as "Patres Conscripti" ("Conscript Fathers"), and the distinction between the two types of senator was lost.
The sum total of the Roman population was divided into two classes, the Senate and the Roman People (as seen in the famous abbreviation SPQR); the Roman People consisted of all Roman citizens who were not members of the Senate, such as the plebeians and proletarians. Domestic power was vested in the Roman People, through the Committee of the Hundreds [Comitia Centuriata], the Committee of the Tribal People (Comitia Populi Tributa), and the Council of the People (Concilium Plebis). Contrary to popular belief, the Senate was not a legislature; a senatus consultum was only a recommendation of legal practice, not a law in and of itself. Actual legislation was vested in the aforementioned Roman assemblies, which acted on the Senate's recommendations and also elected the city's magistrates.
Nevertheless, the Senate held considerable clout (auctoritas) in Roman politics. As the embodiment of Rome, it was the official body that sent and received ambassadors on behalf of the city, that appointed officials to manage the public lands -- including provincial governors, that conducted wars, and appropriated public funds. The Senate also bore the prerogative of authorizing the city's chief magistrates, the consuls, to nominate a dictator in a state of emergency, usually military. In the late Republic, the Senate came to avoid the dictatorate by resorting to a senatus consultum de republica defendenda, the so-called senatus consultum ultimum which declared martial law and empowered the consuls to "take care that the Republic should take no harm", according to Cicero's first In Catilinam oration.
Like the Committee of the Hundreds and the Committee of the Tribal People, but unlike the Council of the People, the Senate operated under certain religious restrictions. It could only meet in a consecrated temple, usually the Curia Hostilia (the ceremonies of New Year's Day were in the temple of Jupiter Optimus Maximus and war meetings were held in the temple of Bellona), and its sessions could only proceed after an invocation prayer, a sacrificial offering, and the auspices were taken. The Senate could only meet between sunrise and sunset, and could not meet while any of the other assemblies was in session.
The Senate had around 300 members in the middle and late Republic, membership could be stripped by the censors if a Senator was thought to have committed an act "against the public morals." Customarily, all magistrates -- quaestors, aediles (both curulis and plebis), praetors, and consuls -- were admitted to the Senate, but not all senators had been magistrates; those who were not were called senatores pedarii and were not permitted to speak, functioning much like the modern parliamentary backbencher. As a result, the Senate was dominated by established families of patricians and plebeians, as it was much easier for these groups to climb the cursus honorum and acquire speaking rights.
Late Republican Senate
In the Late Republic an archconservative faction emerged, led in turn by Marcus Aemilius Scaurus, Quintus Lutatius Catulus, Marcus Calpurnius Bibulus and Cato the younger Marcus Porcius Cato, who called themselves the boni ("The Good Men") or Optimates. The Late Republic was characterized by the social tensions between the broad factions of the Optimates and the nouveau riche Populares, which became increasingly expressed by domestic fury, violence and fierce civil strife; examples of Optimates include Lucius Cornelius Sulla, and Pompey the Great, while Gaius Marius, Lucius Cornelius Cinna and Julius Caesar were Populares.
The consuls alternated monthly as president of the Senate, while the princeps senatus functioned as leader of the house. If both consuls were absent (usually because of a war), the senior magistrate, most often a praetor, would act as the president. Among the senators with speaking rights a rigid order defining who could speak when, with a patrician always preceding a plebeian of equal rank.
There was no limit on debate, and the practice of what is now called the filibuster was a favored trick (a practice which continues to be accepted in the United States Senate today). Votes could be taken by voice vote or show of hands in unimportant matters, but important or formal motions were decided by division of the house; a quorum to do business was necessary, but it is not known how many senators constituted a quorum. The Senate was divided into decuries (groups of ten), each led by a patrician (thus requiring that there would be at least 30 patrician senators at any given time).
Style of dress
All senators were entitled to wear a senatorial ring (originally made of iron, but later gold; old patrician families like the Iulii Caesares continued to wear iron rings to the end of the Republic) and a tunica clava, a white tunic with a broad purple stripe 5 inch (130 mm) wide (latus clavus) on the right shoulder. A senator pedarius wore a white toga virilis (also called a toga pura) without decoration, whereas a senator who had held a curule magistracy was entitled to wear the toga praetexta, a white toga with a broad purple border. Similarly, all senators wore closed maroon leather shoes, but senators who had held curule magistracies added a crescent-shaped buckle. Senators were forbidden to engage in any business unrelated to the ownership of land, but this rule was frequently disregarded.
The Equestrian class
(Until 123 BC, all senators were also equestrians, frequently called "knights" in English works. That year, Gaius Sempronius Gracchus legislated the separation of the two classes, and established the latter as the 300-member Ordo Equester ("Equestrian Order"). These equestrians were not restricted in their business ventures and came from a powerful plutocratic force in Roman politics. Sons of senators and other non-senatorial members of senatorial families continued to be classified as equestrians, who were entitled to wear tunics with narrow purple stripes three inch (75 mm) wide (angustus clavus) as a reminder of their senatorial origins).
Decline of the Senate (1st century BC - 6th century AD)
Julius Caesar introduced a different kind of membership into the Senate during his dictatorate. He increased the membership to 900 and seated many Roman citizens of Latin and Italian background, as well as loyal adherents who had proven their competence and valor during the civil wars. Although intended to break the power of obstreperous reactionary factions like the Good Men, this reform contributed to turning the Senate into a mere cipher, as it became under the Principate and beyond. A remnant of its former self, it continued to figure in Roman politics, but never regained its previous dominance. The Senate survived the end of the Empire in the west, and its last recorded acts were the dispatch of two embassies to the Imperial Court of Tiberius II Constantine at Constantinople in AD 578 and 580.