previous next


IMPE´RIUM and IMPERA´TOR. Imperium is the name of the power attaching to the higher magistrate of the Roman People, as soon as he has been fully installed in office by the passing of a Lex Curiata. It is qualified by the nature of the office to which it appertains (Mommsen, Staatsr. ii.3 p. 845): we have a kingly imperium, a consular imperium, a praetorian imperium, and a dictatorial imperium. In all cases it includes the capacity for both civil and military command. The praetor, for instance, is equally qualified to take command of an army and to administer justice between the citizens ; he does both by virtue of the imperium of his office. The details of the manner in which the imperium operates in the processes of Roman Law will be better discussed under JURISDICTIO Here we have rather to consider the historical and constitutional aspects of the question.

Imperium domi et militiae.--Instead of dividing (as modern states commonly do) the functions of civil and military command, the Romans merely distinguished locally two spheres of [p. 1.996]administration. Outside the walls (militiae, “on service” ) the imperium exists in all its fulness. Its civil and military powers are exercised at pleasure by every provincial governor. Inside the walls (domi) the imperium is, under the Republic, limited by various restrictions; it is subject to the intercessio of a colleague, to provocatio ad populum, and to extinction by the lapse of the period of time assigned to the office. From the year 494 B.C. the imperium at home is likewise crossed by the rival power of the magistrates of the plebs. From all these restrictions the imperium abroad is free. The difference between the two is not sufficient to make military rule absolutely impossible in the city. On the occasion of a triumph the magistrate (unless he be stopped by a tribune) rides with his army through the street. When the city is actually attacked, it must of course be defended by men enrolled under military discipline, and to the magistrate with imperium the command of these men would necessarily belong; unless, however, he got rid of intercessio and provocatio by being nominated dictator, he would be somewhat hampered in the exercise of that command. But under ordinary circumstances the distinction between the two localities was enough practically to exclude military government from the space within the walls, to confine the magistrate “at home” to the civil functions of his imperium, and so to justify the verbal opposition of domi and militiae.

The magistrate legally qualified to act both domi and militiae was further bound by constitutional custom not to confuse the two spheres, but to mark his entry on the freer field of authority by a solemn exit under special auspices, by the change of dress in which he laid aside the gown of peace for the crimson mantle (paludamentum), and by the assumption of the axes which symbolised his enlarged powers. Under the regulations of the later Republic, the occasions on which he was to transfer himself from the one field of government to the other were not left to the discretion of the magistrate, but were marked out for him by the law. The praetor, for instance, who has the urbana provincia assigned to him, must remain at home administering justice. Under Sulla's regulations the same appears to have been the case with the consuls, unless the contrary was ordered by a senatusconsultum “ut exeant paludati” (Cic. Fam. 8.1. 0), which again could be frustrated by the veto of a tribune. On the other hand, this march out must not be put off too long. If the magistrate allows the last day of his year of office to pass while he is still within the walls, his imperium will lapse along with his magistracy. Probably Sulla's law prescribed a precise time in the December of each year for the ceremony. These points are best illustrated by the situation described in Cicero's speech de Provinciis Consularibus, ch. 15; and fully discussed in Mommsen's monograph entitled Rechtsfrage zwischen Caesar und den Senat.

Acquisition of the Imperium.--It would perhaps be going too far to say that the imperium was conferred by a Lex Curiata. We find consuls who have failed to obtain this nevertheless holding the senate and conducting the general business of chief magistrate at Rome. It seems to follow that by virtue of their election they can exercise much of the power of their office, and it is that power which is called imperium. Nevertheless it is clear that some of the main functions appertaining to the imperium could not properly be performed unless the magistrate were empowered by a Lex Curiata. Without this the praetor could not sit in judgment (D. C. 39.19), the consul could not hold the assembly for the election of his successors (D. C. 41.43) nor triumph after a victory (Cic. Att. 4.1. 6, 12). It even seems that he could not without it properly take the command of an army at all ( “consuli, si legem curiatam non habet, attingere rem militarem non licet,” Cic. de Leg. Agr. 2.1. 2, 30). Such rules might, however, be evaded. The Agrarian Law of Rullus (B.C. 63) provided indeed first that a Lex Curiata should be passed for the commissioners, but ordained further that if it were not passed its effects should nevertheless accrue to them. (Cic. ib. 11, 28, “quid postea si ea lata non erit? . . . tum ii decemviri, inquit, eodem jure sint quo qui optima lege.” ) This provision, though Cicero speaks of it as monstrous, could be inserted in any law or plebiscitum creating an extraordinary command. Even in the case of the consul, it was held that the law of Sulla practically dispensed with the necessity for his getting a Lex Curiata before he took command of his province and army. Appius Claudius, consul in 54 B.C., who had been prevented by tribunician intercessio from passing his Lex. Curiata, declared nevertheless (Cic. Fam. 1.9, 25), “se, quoniam ex S. C. provinciam haberet, lege Cornelia imperium habiturum quoad urbem introisset.” The law of Sulla manifestly only repeated the old doctrine [see MAGISTRATUS] that the magistrate cum imperio, though he may be prohibited from exercising his power except in his own provincia, does not lose it (however long the lapse of time) till he comes again within the city walls. But as the law says, “totidem litteris,” that he is to be “cum imperio,” this is held by Appius to confer the imperium by implication. Cicero, though he thinks that Lentulus may have a fighting case if he wishes to dispute the claim of Appius to supersede him, nevertheless is clearly of opinion that this claim is good in law ( “ne id quidem valde dubium est” ).

Collision of Imperium.--The rules as to the collision of imperium, when two magistrates, inferior and superior, are acting in one sphere, are the same as those for the collision of auspices [see MAGISTRATUS]. When two magistrates of equal power are acting together “at home,” their relations are ruled by the principle of intercessio [see MAGISTRATUS]. As the imperium outside the walls is not subject to intercessio, a different principle there obtains. Two equal magistrates must either agree between themselves who is to command (Liv. 22.30, 4), or must divide the army between them (ib. 27, 9), or must take command alternately (ib. 27, 6). In any case there is always some one whom each soldier is bound to obey without question or interference.

Transition to the Principate.--After the Second Punic War the assignment of definite districts to each single magistrate becomes the rule, and a double command is rare. Each [p. 1.997]magistrate or pro-magistrate cum. imperio, having now his locally defined province, is commonly bound not to interfere with his colleagues by exercising any authority in their districts. Nevertheless we have instances in which a coordinate or superior proconsular power is committed to a person other than the proper governor of a province. This infinitum imperium is ascribed by Cicero (in err. 2.3.8, and 3.91.213) to M. Antonius, praetor of 74 B.C., who was commissioned against the pirates. Pompey received it for the same purpose by the Gabinian Law (B.C. 67). Pompey had an “aequum imperium cum proconsulibus” (Vell. 2.31) on any ground within 50 miles of the sea. At a later period (B.C. 57) the imperium infinitum was again granted to Pompey as curator of the corn supply of Rome, and it was even proposed, though not carried, to give him a majus imperium over that of the ordinary governors (Cic. Att. 4.1, 7). Such a superior command was actually voted to the proconsuls Brutus and Cassius in the last days of the Republic. (See Mommsen, Staatsr. ii.3 p. 655.)

The general rule, that the magistrate must govern his province personally, was also broken through in favour of Pompey. From the year 55 B.C. till Caesar's victory at Herda in 49 B.C. he was proconsul of Spain; yet he never set foot in his province, but governed it through legati, while he remained at Rome. In the year 52 he was both consul and pro-consul; for the remaining years he was specially exempted from the rule that the imperium of the promagistrate must lapse, as soon as its holder comes within the city walls.

Pompey set a yet more notable precedent for the system of the Principate, when he lent to Caesar for service in Gaul a legion which had pronounced the sacramentum in his name. The soldiers so lent owed allegiance to Pompey even while serving in Caesar's army; and when the senate required each of the two proconsuls to send a legion for service against the Parthians, Pompey offered as his contribution that one which was in Caesar's camp. Caesar at once acquiesced in the demand.

Proconsulare Imperium of the Principate.--In B.C. 27 the senate assigned certain provinces to Augustus. He governed them, as Pompey had done, by means of legati, who were invested with the subordinate imperium pro praetore. The Emperor remained in the city without forfeiting his proconsular imperium, although it is not clear whether the latter could be exercised over the city itself. Besides his proconsular authority over his own provinces, Augustus had an “infinitum imperium majus,” concurrently with his brother proconsuls in the senatorial provinces (D. C. 53.32, 5; cf. also the case of Germanicus, Tac. Ann. 2.43). The infinitum imperium was especially convenient for the command of the fleet which was concentrated in the hand of Augustus. Lastly, every soldier in the empire had pronounced the sacramentum “in verba Caesaris Augusti.” The precedent of Pompey's Gallic legion was extended to the whole army: all were soldiers of the Emperor. He either commanded them personally or by his legates, or else lent them to his colleagues in the Proconsulare Imperium or to the proconsuls of the senatorial provinces. Germanicus in Germany and Blaesus in Africa have each an independent imperium, but have only borrowed troops. They may command them in the field, but the Emperor retains the sole appointment of the officers, the sole charge of the recruiting, and the sole right to discharge men from the service. If these powers are ever exercised by another person, it is only by delegation from the Emperor (Mommsen, Staatsr. ii.3 pp. 848-851).

The Emperor being regarded as continually a general at the head of his army, not only keeps the insignia commonly associated with the name of Imperator, the laurel wreath and laurelled fasces, but has various prerogatives which may be deduced from those of the Republican general. The guard of honour which escorted the commander in the field attends the Emperor at home, and becomes the garrison of the town of Rome. [See PRAETORIANI] The power of the general to settle his invalided veterans on the lands he has conquered (as Scipio did at the Spanish Italica: Appian, App. Hisp. 38) is interpreted as conferring on the Emperor the right to grant away the ager publicus; and the power of rewarding good service on the part of the auxiliary soldiers by the gift of citizenship (Cic. pro Balbo, 8, 19) develops into the right to make Roman citizens at will.

It is noticeable that the proconsulare imperium, though it was in truth, as Mommsen says (Staatsr. ii.3 p. 840), “the single definite qualification absolutely necessary to the Princeps, and further sufficient by itself alone to constitute the office,” is never mentioned by Augustus himself in the account of his own offices and powers, which is preserved to us in the Monumentum Ancyranum. The assignment of provinces was undoubtedly within the competence of the senate, and it was now held (in extension of the theory propounded by Ap. Claudius) that the senate might therewith confer the power necessary for their government. The official silence gives us to understand that it was a mere matter of administrative arrangement that the charge of certain provinces and armies with the proconsular imperium thereto appertaining was committed to Augustus. [PRINCEPS]

Title of Imperator under the Republic.--Imperator means, of course, “one possessed of the imperium.” Strictly speaking, then, the title should be equally applicable “at home” and “on service.” But from a very early period it was felt to be “uncivil” in the magistrate to flaunt his authority in the face of his fellow-citizens at home. The nickname of Imperiosus applied to a Manlius who had unduly magnified his office (Liv. 7.4, 3) shows the invidious associations of the word. Hence the title of Imperator is never assumed by the magistrate discharging civic functions, nor is the word ever used to describe him. In the army, on the other hand, “Imperator” is the regular mode of address of the soldier to the magistrate under whom he is serving. It is quite clear from Liv. 7.10, 10, and 7.16, 5, that this address was used from the first moment that the general took the field, and not only after a victory. The same may be gathered from Appian's story (Bell. Civ. 4.40) of a proscribed man, Rheginus (who had never, so far as we know, won a victory or [p. 1.998]enjoyed a triumph); one of his old soldiers is described as recognising him with the words: Ἄπιθι χαίρων, αὐτοκράτορ : τοῦτο γάρ μοι προσήκει καὶ νῦν καλεῖν σε.

After a victory it was the custom for the troops to greet their commander with a solemn acclamation. In so saluting they employed their every-day title of address, and the cry “Imperator, Imperator,” sounded from rank to rank. This ceremony relieved the general so honoured from the obligation of veiling his imperium, and stamped upon him the appellation thus publicly uttered. Henceforth he appends the word Imperator to his name, and the title is used even by civilians who have occasion to address him. In the later Republic the senate sometimes gives emphasis to the honourable distinction by itself inviting or sanctioning the assumption of the title by a victorious general. This assumption is commonly the first step towards claiming a triumph. If it befall a man more than once in his life to achieve successes in the field which thus authorise him to advertise his imperium to the world, he sometimes indicates in adverbial phrase the repetition of his honours, and signs himself “Imperator iterum” or “Imperator ter.” Though not every possessor of the imperium is justified in styling himself Imperator, the converse is strictly true; it is impossible for any one to be called Imperator unless he is vested with the imperium. No officer serving under the direct command of another without independent auspices of his own may accept this address (it was refused to the elder Drusus while still only a legate, D. C. 54.33, 5), and no one who has the title can retain it after he lays down his imperium. This occurs for the proconsul the moment he comes within the city walls, unless his imperium be extended for the day of triumph by decree of the people. [See TRIUMPHUS] In this case the title lapses with the imperium after that day.

Use of the title by Caesar.--The elder Caesar during the last fourteen years of his life always styled himself Imperator. There is no reason to suppose that in so doing he overstepped any legal restriction. From the day of his victory over the Helvetii in B.C. 58 down to his death he was continuously vested with the imperium, first as Proconsul, then as Consul (B.C. 48), and then as Dictator. As the imperium never lapsed there was no necessity to lay down the title, though his retention of it in the city was “uncivil” doubtless, and arrogant. The title follows Caesar's name in all official documents. [PRINCEPS]

Praenomen Imperatoris.--With Octavian we come to an entirely new use of the word. In the third year of the triumvirate (B.C. 40) he dropped his praenomen Caius and adopted instead the word Imperator as a praenomen. Side by side with “Marcus Antonius Marci filius” we now find “Imperator Caesar Divi filius.” Mommsen (Staatsr. ii.3 pp. 767-770) has explained this strange transformation in a most ingenious conjecture. He holds that Octavian chose to assume that the title Imperator had so coalesced with the name of Caesar as to have become a sort of honorary cognomen, like Magnus or Africanus. On this assumption he himself would have a hereditary right to his adoptive father's appellation; and once granted that Imperator was a part of the name, it might be transferred at will from the place of cognomen to that of praenomen, just as Nero and Drusus were used as praenomina by several members of the imperial family. Whether we accept this explanation or not, there is no doubt of the fact that Augustus employed the word Imperator as a proper name--ὥσπερ τι κύριον, as Dio Cassius (43.44) says of the emperors of his own time. The next three principes did not adopt the praenomen imperatoris, but retained each his own ordinary praenomen of Tiberius or Caius. With Nero the practice of Augustus was revived, and succeeding emperors likewise assumed this praenomen, some in conjunction with, some in substitution for, the ordinary one.

Salutation Pro Imperio.--Though not every princeps assumed the word Imperator as part of his name, yet every one of them possessed the proconsulare imperium, and was therefore qualified to be addressed as Imperator either by his troops or by the senate. It was the custom at the beginning of each reign for the senate and soldiers to attest their recognition of this qualification in a solemn greeting which exactly follows the precedent of the greeting after a victory. The study of the imperial coins has led the best authorities (see Mommsen, Staatsr. ii.3 p. 782) to the conclusion that, notwithstanding the immense difference in the practical significance of the ceremony in the two cases, the salutation pro imperio and the salutation after a victory are in law precisely the same thing, and that they are counted as similar units by every emperor who signifies the number of his acclamations among his list of honours. Thus, if we find Imp. IV. attached to a name, we are to understand that the sum is made up by one accession to the throne and three victories.

Whensoever the senate thus salutes a man as. Imperator, this is a solemn proclamation that they have either conferred on him (as is their right) the proconsulare imperium, or fully acknowledge him as already invested with it. It is not unnatural that such a salutation by the senate should count as the dies imperii, the day from which the Emperor dates the commencement of his reign. In the register of the sacred college of the Arval Brothers we find a feast “ob diem imperii [Vitellii] . . . Germanici quod xiii. Kal. Mai. statutum est,” and the date is found to synchronise with the day on which the senate heard of the defeat and death of Otho and voted the customary decrees for his successor (Henzen, Acta Fratr. Arv. p. xciv.; Tac. Hist. 2.55; Mommsen, Staatsr. ii.3 p. 842). In the case of Caligula the dies imperii is still more clearly defined. The 18th of March is honoured w<*> a festival, “quod hoc die C. Caesar Augustus Germanicus a senatu Imperator appellatus est” (Henzen, ib. p. xliii.).

The case is different when we find the soldiers giving this salutation to a man who does not possess the imperium which is its legitimate foundation. There are republican precedents to show that this need not in every case be construed as an act of mutiny. In the 7th year of the Second Punic War, after the defeat and, death of P. and Cn. Scipio in Spain, the remnant of the Roman army placed at their head a knight [p. 1.999]named Marcius, who extricated them from their danger. When Marcius sent letters to the senate announcing these events (Liv. 26.2), he signed himself pro praetore, thus assuming that he had de facto acquired the imperium necessary to justify his command of the troops. As he styled himself pro praetore his soldiers would doubtless address him as Imperator, indicating thereby their intention to treat him as if he were their lawful commander. The same lesson may be gathered from the story of the first meeting of Sulla and Pompey. Pompey had on his own authority raised an army in Picenum, had baffled the superior forces opposed to him, and effected a junction with Sulla. When the two met, Pompey of course addressed the victorious proconsul as Imperator: Sulla made use of the same title in reply, thus acknowledging Pompey, not as a mere officer of his own, but as invested with an independent command. In both these cases the de facto imperium was presumed without any intention of rebellion against legal authority, but in obedience to the supposed necessities of the situation, and with the intention of having the assumption afterwards properly ratified. In somewhat the same way under the Principate, troops whose command was vacant by the death of him whose soldiers they had been, might, irregularly but without any gross breach of constitutional order, offer a provisional allegiance to a new commander. This was done by the praetorians to Claudius after the assassination of Caligula. In the present decay of its practical power no choice was left to the senate but to confirm the initiative of the soldiers. This initiative is all the more justified when the person chosen (as Nero, for instance) already possesses the proconsular imperium as colleague of his predecessor. In this case, as no new imperium begins, the event is not counted in the list of acclamations (Mommsen, Staatsr. ii.3 1155). More generally, however, the soldiers in giving this salutation discard a prior allegiance. Here, too, we may find an early parallel in the story told by Livy (7.39), of a military insurrection during the Samnite War. The mutineers seized on a retired officer named Quinctius, and offered him the choice of death or imperium et honorem. Forced to submit, he was at once saluted “Imperator,” and carried to the camp. In like manner when the army of Germany, for instance, greeted its legate Vitellius as Imperator, this acclamation was an act of revolution and civil war. It ascribed the proconsulare imperium to one who not only did not already possess it, but who could not possess it without supplanting his legal commander. It further proclaimed the intention of these soldiers to prove their assertion good at the point of the sword.

Vitellius, as we have already seen, dated his reign not from this first salutation, but from the day when his authority was acknowledged by the senate. It was no doubt the more correct and more modest proceeding that the Emperor should thus ignore the irregular inception of his reign, and refer his power to the moment when it was legitimately conferred. But we also find another theory prevalent. From the moment when the pretender has accepted from any voice the salutation of Imperator, he has claimed to be in possession of the magisterial authority which serves as a basis for that title. If these pretensions are afterwards made good, he may without any great breach of propriety look upon them as having received a retrospective sanction, and may refer back to the moment of claim as the moment of acquisition. So we are told (Suet. Vesp. 6) that Vespasian kept as his dies imperii the day (July 1st) when he was first saluted Imperator by the legions of Egypt, though for months later the senate and the city of Rome were under the control of his rivals.

History of the Title under the Principate.--The supreme importance of the proconsulare imperium and of the functions attached to it added lustre to the derived name of Imperator. It might indeed attach to other persons than the reigning princeps. The Emperor's colleagues might accept the solemn salutation after a. victory and assume the title of honour. Tacitus tells us (Ann. 1.3) that Augustus “privignos imperatoriis nominibus auxit,” and again (2.26) of the younger Drusus, that he “nonnisi apud Germanos assequi nomen imperatoris et deportare lauream posse.” The title is frequent on their coins, and the word is sometimes used to describe them (Tac. Ann. 2.17, 2; 3.12, 4). It is also clear that Imperator was the everyday mode of address which the soldiers used towards them no less than towards the princeps. Velleius tells (2.104) that when Tiberius was sent by Augustus to take command of the army of Pannonia, his old soldiers crowded round him, exclaiming, “Videmus te, Imperator, salvum recepimus . . . ego tecum, Imperator, in Armenia,” &c. The same was probably the case with the senatorial proconsuls of Africa. The soldiers would not have been likely publicly to salute Blaesus Imperator, as they did after his victory over Tacfarinas (Tac. Ann. 3.74), unless they had been used to call him by that name in private. On this occasion Tiberius allowed to Blaesus the assumption of the title, but the precedent was not afterwards followed. By the time of Domitian the word had become so distinctive an emblem of the supreme power that an unfortunate senator was put to death because by a slip of the tongue on the part of the crier he had been proclaimed Imperator instead of Consul. Gradually the proconsular and military associations connected with the words “imperium” and “imperator” fall away. In the jurists of the 2nd century “imperium” and “imperatoria potestas” denote the whole of the powers conferred on the chief of the state (Mommsen, Staatsr. ii.3 p. 877, n. 1). “Imperator” becomes the title of the chief magistracy, and to a great extent supplants that of “princeps” by which Augustus had chosen to describe himself.


hide References (20 total)
  • Cross-references from this page (20):
    • Cicero, Letters to his Friends, 1.9
    • Cicero, Letters to Atticus, 4.1
    • Cicero, Letters to Atticus, 4.1.6
    • Cicero, Letters to Atticus, 4.7
    • Appian, Wars in Spain, 7.38
    • Cicero, On the Agrarian Law, 2.1.2
    • Tacitus, Annales, 3.74
    • Tacitus, Annales, 2.17
    • Tacitus, Annales, 2.2
    • Tacitus, Annales, 2.43
    • Tacitus, Annales, 3.12
    • Tacitus, Annales, 3.4
    • Tacitus, Historiae, 2.55
    • Livy, The History of Rome, Book 26, 2
    • Livy, The History of Rome, Book 7, 10
    • Livy, The History of Rome, Book 7, 3
    • Livy, The History of Rome, Book 7, 39
    • Livy, The History of Rome, Book 7, 4
    • Livy, The History of Rome, Book 22, 30
    • Livy, The History of Rome, Book 22, 4
hide Display Preferences
Greek Display:
Arabic Display:
View by Default:
Browse Bar: