With the abolition of the Roman monarchy in 509 BC, the imperium, or executive power, of the king was divided between two annually-elected magistrates, known as praetors. In time they would come to be known as consuls, although probably not until the creation of a third, junior praetor in 367 BC. Neither consul was superior to the other, and the decisions of one could be appealed to the other (provocatio). Their insignia were the toga praetexta and the sella curulis, and each was attended by an escort of twelve lictors, each of whom bore the fasces, a bundle of rods topped by an axe; but by custom the lictors had to remove the axes from their fasces within the pomerium, the sacred boundary of Rome, to signify that the people, and not the consuls, were sovereign.
After several years, the fear of impending war with both the Sabines and the Latin League, combined with widespread suspicion that one or both of the consuls favoured the restoration of the monarchy, led to the call for a praetor maximus, or dictator ("one who gives orders"), akin to the supreme magistrate of other Latin towns. According to most authorities, the first dictator was Titus Lartius, who appointed Spurius Cassius his magister equitum.
Although there are indications that the term praetor maximus may have been used in the earliest period, the official title of the dictator throughout the history of the Republic was magister populi, or "master of the infantry". His lieutenant, the magister equitum, was the "master of the horse" (that is, of the cavalry). However, the use of dictator to refer to the magister populi seems to have been widespread from a very early period.
The appointment of a dictator involved three steps: first, the Senate would issue a decree known as a senatus consultum, authorizing one of the consuls to nominate a dictator. Technically, a senatus consultum was advisory, and did not have the force of law, but in practice it was nearly always followed. Either consul could nominate a dictator. If both consuls were available, the dictator was chosen by agreement; if they could not agree, the consuls would draw lots for the responsibility. Finally, the Comitia Curiata would be called upon to confer imperium on the dictator through the passage of a law known as a lex curiata de imperio.
A dictator could be nominated for different reasons, or causa. The three most common were rei gerundae causa, "for the matter to be done", used in the case of dictators appointed to hold a military command against a specific enemy; comitiorum habendorum causa, for holding the comitia, or elections, when the consuls were unable to do so; and clavi figendi causa, an important religious rite involving the driving of a nail into the wall of the Temple of Jupiter Optimus Maximus, as a protection against pestilence. Other reasons included seditionis sedandae causa ("to quell sedition"); ferarium constituendarum causa (to establish a religious holiday in response to a dreadful portent); ludorum faciendorum causa (to hold the Ludi Romani, or "Roman Games", an ancient religious festival); quaestionibus exercendis, (to investigate certain actions); and in one extraordinary case, senatus legendi causa, to fill up the ranks of the Senate after the Battle of Cannae. These reasons could be combined (seditionis sedandae et rei gerundae causa), but are not always recorded or clearly stated in ancient authorities, and must instead be inferred.
In the earlier period it was customary to nominate someone whom the consul considered the best available military commander; often this was a former consul, but this was never required. However, from 360 BC onward, the dictators were usually consulares. Normally there was only one dictator at a time, although a new dictator could be appointed following the resignation of another. A dictator could be compelled to resign his office without accomplishing his task or serving out his term if there were found to be a fault in the auspices under which he had been nominated.
Like other curule magistrates, the dictator was entitled to the toga praetexta and the sella curulis. He received a ceremonial bodyguard that was unique in Roman tradition: "[t]wenty-four lictors indicated his quasi-regal power, which, however, was rather a concentration of the consular authority than a limited revival of the kingship."
In a notable exception to the Roman reluctance to reconstitute the symbols of the kings, the lictors of the dictator never removed the axes from their fasces, even within the pomerium. Symbolizing their power over life and death, the axes of a dictator's lictors set him apart from all other magistrates. In an extraordinary sign of deference, the lictors of other magistrates could not bear fasces at all when appearing before the dictator.
As the kings had been accustomed to appear on horseback, this right was forbidden to the dictator, unless he first received permission from the comitia.
In addition to holding a military command and carrying out the actions decreed by the Senate, a dictator could summon the Senate or convene one of the legislative assemblies of the Roman people. The full extent of the dictatorial power was considerable, but not unlimited. It was circumscribed by the conditions of a dictator's appointment, as well as by the evolving traditions of Roman law, and to a considerable degree depended on the dictator's ability to work together with other magistrates. The precise limitations of this power were not sharply defined, but subject to debate, contention, and speculation throughout Roman history.
In the pursuit of his causa, the dictator's authority was nearly absolute. However, as a rule he could not exceed the mandate for which he was appointed; a dictator nominated to hold the comitia could not then take up a military command against the wishes of the Senate. Some dictators appointed to a military command also performed other duties, such as holding the comitia, or driving a nail into the wall of the Temple of Jupiter Optimus Maximus; but presumably they did so with the Senate's consent.
The imperium of the other magistrates was not vacated by the nomination of a dictator. They continued to perform the duties of their office, although subject to the dictator's authority, and continued in office until the expiration of their year, by which time the dictator had typically resigned. It is uncertain whether a dictator's imperium could extend beyond that of the consul by whom he was nominated; Mommsen believed that his imperium would cease together with that of the nominating magistrate, but others have suggested that it could continue beyond the end of the civil year; and in fact there are several examples in which a dictator appears to have entered a new year without any consuls at all, although some scholars doubt the authenticity of these dictator years.
Initially a dictator's power was not subject to either provocatio, the right to appeal from the decision of a magistrate, or intercessio, the veto of the tribunes of the plebs. However, the lex Valeria, establishing the right of appeal, was not abrogated by the appointment of a dictator, and by 300 BC even the dictator was subject to provocatio, at least within the city of Rome. There is also evidence that the power of the plebeian tribunes was not vitiated by the dictator's commands, and 210 BC, the tribunes threatened to prevent elections held by the dictator, Quintus Fulvius Flaccus, unless he agreed to withdraw his name from the list of candidates for the consulship.
A dictator was expected to resign his office upon the successful completion of the task for which he was appointed, or at the expiration of six months. These sharp limitations were intended to prevent the dictatorship from too closely resembling the absolute power of the Roman kings. But the six month limitation may have been dispensed with when the Senate deemed it expedient; no consuls are known for the years 333, 324, 309, and 301, and it is reported that the dictator and magister equitum continued in office without any consuls.
Most authorities hold that a dictator could not be held to account for his actions after resigning his office, the prosecution of Marcus Furius Camillus for misappropriating the spoils of Veii being exceptional, as perhaps was that of Lucius Manlius Capitolinus in 362, which was dropped only because his son, Titus, threatened the life of the tribune who had undertaken the prosecution. However, some scholars suggest that the dictator was only immune from prosecution during his term of office, and could theoretically be called to answer charges of corruption.
The dictator's lieutenant was the magister equitum, or "master of the horse". He would be nominated by the dictator immediately upon his own appointment, and unless the senatus consultum specified the name of the person to be appointed, the dictator was free to choose whomever he wished. It was customary for the dictator to nominate a magister equitum even if he were appointed for a non-military reason. Before the time of Caesar, the only dictator who refused to nominate a magister equitum was Marcus Fabius Buteo in 216 BC, and he strenuously objected to his own nomination, because there was already a dictator in the field.
Like the dictator, the magister equitum was a curule magistrate, entitled to the toga praetexta and the sella curulis. His imperium was equivalent to that of a praetor (in the later use of the term), in that he was accompanied by six lictors, half the number accorded to the consuls. But like the dictator, he could summon the Senate, and probably also the popular assemblies. His authority was not subject to recall, although if the dictator were compelled to resign due to a fault in the auspices, the magister equitum was also expected to resign, and when the dictator laid down his imperium, so would the magister equitum.
In theory, the magister equitum was commander of the cavalry, but he was not limited to that role. The dictator and magister equitum did not always take the field together; in some instances the magister equitum was assigned the defense of the city while the dictator took an army into the field, while on other occasions the dictator remained at Rome to see to some important duty, and entrusted the magister equitum with an army in the field. The magister equitum was necessarily subordinate to the dictator, although this did not always prevent the two from disagreeing.
During the first two centuries of the Republic, the dictatorship served as an expedient means by which a powerful magistracy could be created quickly in order to deal with extraordinary situations. Created for military emergencies, the office could also be used to suppress sedition and prevent the growing number of plebeians from obtaining greater political power. In the Conflict of the Orders, the dictator could generally be counted upon to support the patrician aristocracy, since he was always a patrician, and was nominated by consuls who were exclusively patrician. After the lex Licinia Sextia gave plebeians the right to hold one of the annual consulships, a series of dictators were appointed in order to hold elections, with the apparent goal of electing two patrician consuls, in violation of the Licinian law.
After the Second Samnite War, the dictatorship was relegated almost exclusively to domestic activities. No dictator was nominated during the Third Samnite War, and the six-month limitation on its powers made the dictatorship impractical for campaigns beyond the Italian peninsula. In 249 BC, Aulus Atilius Calatinus became the only dictator to lead an army outside Italy, when he invaded Sicily, and he was the only dictator to hold a military command during the First Punic War. The last dictators to lead an army in the field were Quintus Fabius Maximus Verrucosus in 217, and Marcus Junius Pera the following year, during the early stages of the Second Punic War. All of the other dictators appointed during that conflict remained at Rome in order to hold the comitia; the last dictator named in the traditional manner was Gaius Servilius Geminus, in 202 BC.
For the next century, Rome's ordinary magistrates and promagistrates successfully carried on all Roman campaigns, without the need for a dictator, and the office fell into abeyance. Then, in 82 BC, the dictatorship was suddenly revived by Sulla. Sulla, already a successful general, had previously marched on Rome and taken the city from his political opponents six years earlier; but after he permitted the election of magistrates for 87, and departed to campaign in the east, his enemies returned. In 83 he turned his attention to regaining Rome, and after defeating his opponents decisively the next year, the Senate and the people named him dictator legibus faciendis et rei publicae constituendae, giving Sulla the power to rewrite the Roman constitution, without any time limit.
Sulla doubled the size of the Senate from 300 to 600, filling its ranks with his supporters. He then placed severe limits on the tribunician power, limiting the veto and forbidding ex-tribunes from holding higher magistracies. Although he resigned the dictatorship in 81, and held the consulship in 80, before returning to private life, Sulla's actions had weakened the Roman state and set a precedent for the concentration of power without effective limitation.
The dictatorial power was then granted to Caesar in 49 BC, when he returned to Rome from his campaigns in Gaul, and put the forces of Pompeius to flight. He resigned the dictatorship after only eleven days, having held the comitia at which he himself was elected consul for the following year. Late in 48, Caesar was named dictator rei gerundae causa with a term of one year, and granted the tribunician power for an indefinite period. He saw to the impeachment of two tribunes who had tried to obstruct him, and having been granted censorial powers, he filled the depleted numbers of the Senate with his supporters, raising the number of senators to 900. In 47, he was named dictator for a term of ten years. Shortly before his assassination in BC 44, Caesar was named dictator perpetuo rei publicae constituendae, and given the power to appoint magistrates at will.
Caesar's murder came at the hands of conspirators who presented themselves as saviours of the Republic. In order to maintain popular support, Caesar's followers took great care to show their own commitment to preserving the Roman state. The month after the assassination, Mark Antony, who had been Caesar's magister equitum in BC 47, proposed a series of laws, confirming Caesar's actions, but allowing appeals and formally abolishing the dictatorship. These were passed, as the leges Antoniae.
In 23 BC, when Caesar's nephew and heir Augustus had attained full control of the state, the Senate offered to appoint him dictator, but he declined, while at the same time accepting proconsular imperium and the tribunician power for life. Thus, Augustus preserved the appearance of respecting Republican forms, even as he arrogated most of the powers of the Roman state. Following his example, none of the emperors who succeeded him ever adopted the title of dictator. When Constantine chose to revive the ancient concept of the infantry commander, he pointedly gave the office the name of magister peditum, "master of the foot", rather than magister populi, the official style of a dictator.