Tribune
Military tribunes (tribuni militum) were originally infantry commanders. Under the early republic there were six to a legion; some were appointed by the consuls (chief executives) or military commanders, and others were elected by the people. Under the empire (after 27 bc) the military tribunate was a preliminary part of a senatorial or an equestrian career and subject to the emperor’s nomination. Tribunes commanded bodyguard units and auxiliary cohorts.
The tribuni plebis (tribunes of the plebs, or lower classes) were in existence by the 5th century bc; their office developed into one of the most powerful in Rome. The exact date of its institution, the original mode of election, and the original extent of its powers are uncertain. From 471 bc the tribunes of the plebs were elected in the plebeian assembly (concilium plebis), over which they presided, and thus could express, and agitate for, plebeian demands. Their power was exercised through the veto (intercessio), which could invalidate the acts of consuls and lower magistrates and of their own colleagues. Their persons were legally inviolable. By 450 they were 10 in number. It was their duty to protect persons against the acts of magistrates, but they could also initiate prosecutions of offenders against the state. From 300 bc most legislation was introduced by tribunes because the legislative process in the plebeian assembly was less cumbersome than in the centuriate assembly (see comitia). After 287 bc, when the people they represented began to rise in the social scale, some tribunes began to use their powers to thwart more sweeping popular proposals. Others, like Gaius and Tiberius Gracchus in the 2nd century bc, continued to champion them, even in the area of land reform and debtor relief. Their powers were curtailed by Sulla, then restored by Pompey in the 1st century bc. Under the empire (after 27 bc) the tribunes themselves were without authority, but the “tribunician power” (tribunicia potestas) was held by the emperor, and was a major element in his authority. By virtue of it, he had personal inviolability, could veto measures freely, summon the organs of government, and propose decrees and legislation. He numbered the years of his power by it, thus exploiting to the full the old democratic tradition of the champion of the plebs.
Treasury tribunes (tribuni aerarii) were probably originally the officials who collected the tribute and distributed the soldiers’ pay in the tribes. After 168 bc they remained a distinct order ranking below the equites