The exercise of authority in Rome – at least during much of the Republic – things changed under the Principate and the Empire – was based, as were morals and religion upon the mos maiorum, the laws of the elder, and Roman society was very much a mirror image of its core, the family.
The family – which rather should be translated as “household” than referring to the blood relatives only – was almost dictatorily headed by the pater familias, while the relations outside of the family were guided by the principles of patron (patronus) and client (cliens).
It surprises little that these two elements were largely mirrored within the legal concepts of civil and military authority.
The concept of potestas was applied, as we would say, in matters of the private law, within the family as the Patria potestas, and in civil law the power, or perhaps better the jurisdiction and responsibility, of a magistrate to promulgate the laws and arrange the workings of the state, i.e. rather an expression of socially recognized power than an executive function.
Auctoritas, however, was different in nature, not a matter of the law but a measure of the prestige a man (or, in Imperial times, a woman) enjoyed within the Roman society. Politically, it expressed itself predominantly in the Senate, in the auctoritas of the Princeps Senatus, the censors, and other outstanding personalities. (1) It was, naturally, a matter of charisma.
Imperium was a more serious matter. It was the legally prescribed formal power of command a citizen held over a civil or military entity – a military unit, a province, territory, campaign or special command (e.g. Pompey against the Cilician pirates in 67-66 BC). Imperium was held by the curule aedile, the praetor, the consul, the magister equitum, and the dictator, and such promagistrates (propraetors and proconsuls) which were appointed annually for the government of provinces.
Imperium was bestowed by a legal act of the Senate and originally limited to one year with the exception of the dictator’s term of six months and the rare imperium maius which could last as long as the underlying mandate. In the last century of the Republic, these rules were commonly broken – Marius‘ seven consulships, Caesar‘s five-year term in Gallia and his and Sulla‘s dictatorships. The emperors’ Imperium, naturally, ran for a lifetime.
Imperium included – at least in principle – the power to command everything up to the death penalty for offenders (although various laws limited the death penalty for Romans citizens, which, however, tended to work better for the rich and famous than for the poor sods of Subura and the bottom of Esquilina, the two tribes reserved for the majority of the plebs).
Since many magistrates held Imperium, the question of overruling was a constant practical matter. Commonly it worked by seniority – an aedile could be overruled by a praetor, the praetor by the consul and so forth. Colleagues could overrule each other, i.e. veto – and frequently did, except for the dictator, whose orders were above the law and not subject to subsequent judicial proceedings.
In special cases – see Pompey above – the Senate could give out imperium maius (“greater”) to an official, usually for a closely defined task (dictators held it by definition). This proved such a desirable and effective method of office that it was quickly appropriated by the emperors and became their hallmark.
Tiberius and Gaius Gracchus, the two famous tribunes, by Eugene Guillaume
The last and rather different form of a command – being entirely a negative power – was the famous “Intercessio!” – ‘I step in!’, by which any Tribune of the Plebs (of which they were usually ten) could veto discussions, commands, trials and even laws. This being a most practical way of interference, every bigwig of the late republic – Marius, Sulla, Pompey, Caesar and the like – made sure they always had one or two tame tribunes on their payroll which they could use for political sabotage.
This ability proved so useful and desirable that, from Augustus on, every emperor made sure to receive the tribunal character on the occasion of his ascension to the throne. Imperium maius and the tribunal power became the major instruments of Imperial reign.
(© John Vincent Palatine 2019)
(1) See Wiki: The 19th-century classicist Theodor Mommsen describes the “force” of auctoritas as “more than advice and less than command, a piece of advice which one may not safely ignore.” Cicero says of power and authority, “Cum potestas in populo auctoritas in senatu sit.” (“While power resides in the people, authority rests with the Senate.”)