Princeps senatus is a good example of the inventiveness and evolution of Roman political system. The office was outside cursus honorum, didn’t have any imperium and was only open to patricians. The appointment was for 5 years and so each new pair of censores appointed their choice to be princeps.
The real power of the position and source for its immense prestige was that the princeps senatus held the right to speak first in given subject in the Senate. According to the Roman system and how the Senate session worked, the first speaker managed usually control the ensuing debate by his speech – all the more if he was an accomplished orator. Gradually also other privileges were added for the position e.g. summoning and adjourning the senate meeting. Something of the prestige and meaning of the title for the Romans is that princeps is the title Augustus and his successors choose for themselves.
Here is the list of known principes senatus from 150 – 50, or actually until 89, because after that we do not have reliable records. As it is, even while the office was the peak of career and only accessible for a patrician, we have very incomplete information of the principes.
153/152 – 147 nemo
147 – ? P. Cornelius Scipio Nasica Corculum
? – ? ?
136 – 130Ap. Claudius Pulcher
130 – ? L. Cornelius Lentulus Lupus
125? – ?P. Cornelius Lentulus
115 – 89 M. Aemilius Scaurus
After 179 – 153/152 M. Aemilius Lepidus (cos 187) the office was vacant until 147, when Scipio Nasica Corculum, a son of cousin of Scipio Africanus (Scipio the Elder) and also a husband of his daughter, was appointed into it. Scipio Africanus had held the position at 199 – 184/183. Scipio Nasica Corculum began his term at 147, so his term should have ended at 142/141. We know he died 141, so probably there was someone appointed after him and before Ap. Claudius Pulcher (cos 143).
The appointment of Ap. Claudius Pulcher is in many ways a prime example of the position and eligability for it. Pulcher was not the most senior statesman when he was appointed. At first this seems to contradict the very idea of the position. Consul of 156 L. Cornelius Lentulus Lupus was the most senior patrician ex-censor living and as such a natural choice for the position. Also Scipio Africanus Aemilianus (Scipio the Younger) was alive and active, and as the destroyer of Carthage and otherwise highly accomplished citizen, he would have made a very natural choice for the most prestigious position of the republic. Ap. Claudius Pulcher on the other hand was not a military genious (you can read more about his triumph here) and certainly not senior in years compared to Lupus and Scipio. What then he did possess to justify the appointment?
Ap. Claudius Pulcher was a very ambitious politician. He evidently worked hard to form political alliances in old Roman way and to gather support in appearing at the Forum. There is even an anecdote of his verbal jousting during his first campaign for censor against Scipio Aemilianus, no other. Pulcher said to Scipio, that Scipio hardly knew anyone at the Forum (stinging against Scipio’s way of not frequenting at Forum), to which Scipio replied that Pulcher had got it right, because Scipio didn’t live his life to know many people, but to be unknown to no-one (which of course was sting against Pulcher, who could not match anywhere near the military glory and fame of Scipio). Scipio carried the election and was elected as censor in 142 and Pulcher had to wait until next time to be elected at 136.
Pulcher built his support base for a long time in many methods and his appointment as princeps can be seen as a culmination of his efforts. Pulcher’s daughter was married to Ti. Gracchus. C. Grcchus, Tiberius’ brother, was married to daughter of P. Licinius Crassus Mucianus, who with his biological brother P. Mucius Scaevola, supported Gracchus and Claudius at 133. The other daughter of Mucianus was married to the Ser. Sulpicius Galba, the most famous orator of his time. It was Galba who in 149 had defended Q. Fulvius Nobilior, who was the censor to appoint his colleague Pulcher as princeps senatus. All these persons were in opposition to Scipio.
So what Pulcher had, was the traditional extended and many layered network of contacts, friends, allies and services and counter services that made the Roman political life so complicated and dynamic environment. Scipio lacked this broad political support throughout the Senate. In this sense the system worked perfectly: only a candidate with wide support at each corner of the Senate could be appointed as princeps senatus – to reflect the broad consensus of the senate as the first speaker. No outsider or upstart could convince the system otherwise – not even the celebrated second Africanus.
It’s interesting to note that Cornelius Lentulus Lupus got his turn as princeps senatus after Ap. Claudius Pulcher, but Scipio never did. This underlines the fact that no loner could reach the peak position of the republic, there was everything else than lonely at the top: to get into office of princeps senatus and to get to set the tone in each senate discussion, you had to be a master networker. This I think tells the essence of what being princeps senatus was about.