The princeps senatus (plural principes senatus) was the first member by precedence of the Roman Senate. Although officially out of the cursus honorum and owning no imperium, this office brought enormous prestige to the senator holding it.
The princeps senatus was not a lifetime appointment. He was chosen by every new pair of censors (that is, every 5 years). Censors could, however, confirm a princeps senatus for a period of another 5 years. He was selected from patrician senators with consular rank, usually former censors. The successful candidate had to be a patrician with an impeccable political record, respected by his fellow senators.
Originally, the position of the princeps was one of honor: he had the privilege of speaking first on the topic presented by the presiding magistrate. This gave the position great dignitas as it allowed the princeps to set the tone of the debate in the Senate. In the late Republic and in the Principate, the office gained the prerogatives of the presiding magistrates and additional powers, namely:
Summoning and adjourning the Senate
Deciding its agenda
Deciding where the session should take place
Imposing order and other rules of the session
Meeting, in the name of the Senate, with embassies of foreign countries
Writing, in the name of the Senate, letters and dispatches
^ Said also to have succeeded his father as Princeps Senatus in 265 BC.
^ Duilus is unlikely to have been Princeps Senatus; he was consul in 258 BC with the patrician Lucius Cornelius Scipio which was a rare honour for a novus homo (New Man) like him.
^ Probably Manius Valerius Maximus Corvinus Messalla, who was consul in 263 BC and censor in 252 BC. Marcus Valerius Messalla, probably his son, was too young and obscure in 225 BC.
^ Fabius Maximus's choice as Princeps Senatus caused a dispute that year between the censors Publius Sempronius Tuditanus and Marcus Cornelius Cethegus. Cethegus favoured the mos maiorum which required that the most senior ex-censor (in terms of the year of his censorship) should be chosen. This was Titus Manlius Torquatus. Tuditanus favoured the most distinguished man alive, who in his opinion was Fabius Maximus. Tuditanus had the right to choose or to cast the deciding vote, and thus Fabius was made Princeps Senatus. (Source: Livy). This decision, to break or bend the mos maiorum, would have consequences when Scipio Africanus, a much younger man, was chosen in 199 BC.
^ Scipio Africanus was the first known censor to be proposed by his co-censor, shortly after being elected to the censorship. It is not clear if he was removed from office before he died, but by 184 BC he had retired into private life far from Rome and was in ill health.
^ Scipio was certainly not the most senior living censor in 199 BC, with several ex-censors alive. However, Paetus relied on the precedent set in 209 BC by Tuditanus in choosing the most distinguished Roman ex-consul alive.
^ Flaccus was the second known censor to be elected (exact year not known), presumably by his co-censor
^ Lepidus was the third known censor to be elected, presumably by his co-censor.
^ Some sources claim that Scipio Nasica was removed from office as Princeps Senatus when the Third Punic War broke out and he lost his political influence. Scipio Nasica had served as censor in 159 BC; whether he was the most senior censor alive (in terms of year of censorship) is unknown.
^ Pulcher was the fourth known censor to be elected, presumably by his co-censor.
^ Scaurus was the first Princeps Senatus to be elected to the title, who was not yet censor; he became censor briefly in 109 BC and had to be forced to resign after his co-censor Marcus Livius Drusus died suddenly. He was also not yet consul; thus his elevation to the rank of Princeps Senatus is remarkably puzzling. Historians suggest that he was the most senior living patrician senator, but this is uncertain.