INTERCESSIO. — In Roman public law, intercession begins with the foundation of the Republic and initially signifies the right of one of the consuls to prevent, by virtue of the par potestas, an act performed by the other consul from producing legal consequences.
The concept of intercession is intimately linked to that of collegiality. When new magistracies were subsequently created, the right of intercession existed not only between colleagues, but the superior magistrate, by virtue of his maior potestas, could use intercession to intervene against measures adopted by the inferior magistrate. The consul could therefore intercede against the acts of every other magistrate, and the praetor could likewise do so with respect to magistrates inferior to him. However, while the higher magistrates could intercede against those holding a high position in the cursus honorum, as well as against the lower magistrates, no intercession took place among the latter, despite their hierarchical ordering. The censor, moreover, occupied a particular position: he could not oppose others, nor could intercession be exercised against him.
To these limitations on the powers exercised among magistrates, another form of intercession was added with the institution of the tribunes of the plebs in 487; this was subsequently the most frequently used form. The tribunes of the plebs were not magistrates, but, being endowed with the right of auxilium in defence of the interests of the plebs, they could intercede against the acts of any magistrate (with the obvious exception of the dictator), against the provisions of senatusconsulta, and against the rogationes submitted to the vote of the assemblies. This intercession by the tribunes was the form that received the widest application. It is understood, however, that such a right could be exercised only within the city and its immediate surroundings. Acts performed by a magistrate endowed with imperium to be exercised outside the pomerium were therefore exempt from intercession.
Under the Empire, the right of intercession belonged above all to the emperor by virtue of his tribunica potestas, and belonged to him in a broader form than previously—not only because the tribunica potestas ultimately became a lifelong power, but also because it was valid not merely for the city of Rome but throughout the Empire, and could not be countered by the intercession of another tribune of the plebs, since there was no collegiality between the tribune of the plebs and the prince invested with the tribunica potestas. In the first century of the Empire, there is evidence of instances of intercession by the emperor and, much more rarely, even of intercession by tribunes of the plebs against the acts of magistrates; subsequently, the former was suppressed, while the latter became superfluous with the consolidation of imperial absolutism.