In ancient Rome a promagistrate (Latin: pro magistratu) was an ex-consul or ex-praetor whose imperium (the power to command an army) was extended at the end of his annual term of office or later. They were called proconsuls and propraetors. This was an innovation created during the Roman Republic. Initially it was intended to provide additional military commanders to support the armies of the consuls (the two annually elected heads of the Republic and its army) or to lead an additional army. With the acquisitions of territories outside Italy which were annexed as provinces, proconsuls and propraetors became provincial governors or administrators. A third type of promagistrate were the proquaestors.
The first type of promagistrate was the proconsul. In the early days of the Roman Republic, when Roman territory was small, Rome had only two legions, each commanded by one of the two consuls. Rome was continually under attack by neighboring peoples (the Etruscans in the north, the Sabines in the east and the Volsci and Aequi in the south). Dionysius of Halicarnassus recorded five instances when a proconsul was appointed between 480 BC and 464 BC. In 480 BC a proconsul led the left wing of an army which combined the two consular legions while the consuls led the centre and the other wing. In 478 BC two proconsuls are mentioned. One served under the consul who went to fight the Etruscans in the north. Another one commanded a third legion. An extra legion was deployed so that two enemies in the south (the Volsci and Aequi) could be confronted individually with two armies. In 464 BC a proconsul led an irregular force of volunteers and reservists to support a consul whose army was insufficient to match the combined forces of two enemies. Dionysius did not specify the role of the proconsuls on the other occasion. Dionysius described these men as 'legates and proconsuls,' which implied proconsular imperium was directly delegated by the incumbent consul and that the proconsul acted as a sort of deputy of the consul in the military action. It was a temporary measure adopted to deal with an immediate military emergency. In the last of the mentioned occasions, the proconsul was appointed by a decree of the senate and Livy noted that this "form of a decree has ever been deemed to be one of extreme exigency." It seems that in these instances an extra commander was drawn from men who had previously been consuls because they had prior experience of commanding an army.
The concept of promagistracy originally involved the notion of the promagistrate acting on behalf of a magistrate: pro consule (one behalf of the consul), pro preaetore (on behalf of the praetor). However, in practice this changed when there was a more regular need to create additional military commanders. In 366 BC the office of the praetor was created. This was the city's chief justice. He also had the power to command an army. During the Second Samnite War (326–304 BC) Rome increased the number of its legions. Several proconsuls were appointed to conduct specific operations. Proconsular imperium became an extension (prorogatio) of the imperium of a consul. During the Third Samnite War (298–290 BC) the propraetors were also created. These were praetors whose imperium was extended and who were given the task of commanding reserve armies. Prorogatio was the extension imperium beyond the one-year term of the consul or praetor. It was a dispensation from the limit of the existing term of office which applied only outside the city walls of Rome. It did not have effect within the city walls. Therefore, it was an exertion of the military command of the consul or praetor, but not of his public office. It was an exclusively military measure.
As Rome acquired territories beyond Italy which she annexed as provinces there was a need to send governors there. In 227 BC, after the annexation of the first two Roman provinces, (Sicilia in 241 BC and Corsica et Sardinia in 238 BC), two praetors were added to the two praetors who acted as chief justices in the city of Rome and were assigned the administration of these two provinces. Two more praetors were added when the provinces of Hispania Citerior and Hispania Ulterior were created in 197 BC. After this no new praetors were added even though the number of provinces increased. The Romans began to extend the imperium of the consuls and the praetors in Rome at the end of their annual term. The provinces were assigned by lot to the proconsuls and propraetors. The proconsuls were given the provinces which required a larger number of troops. A promagistrate held equal formal status to the equivalent magistrate and was attended by the same number of lictors.
In 81 BC Lucius Cornelius Sulla added two new praetors so that two proconsuls and six propraetors could be created to govern the ten provinces Rome had acquired by then. The praetors who had previously governed the first four provinces were reassigned to judicial affairs in Rome as the judicial load in the city had increased. Sulla made the governorships annual and required the holder to leave the province within thirty days after the arrival of his successor. In 52 BC Pompey introduced a law which provided that the promagitracies were to be assigned five years after the term of office of the consuls and praetors. Julius Caesar repealed it. Pompey's provision was re-enacted by Augustus.
The concept of delegated authority was sometimes used to confer proconsular imperium on someone who had never held consular power before. During the Second Punic War (218–201 BC) Publius Cornelius Scipio Africanus volunteered to lead the second Roman expedition against the Carthaginians in Hispania. He was too young to have been a consul. Therefore, proconsular imperium was bestowed on him by a vote of the people. This was an extraordinary measure, but it set a precedent. When Scipio left Hispania after his victory in 205 BC, Lucius Cornelius Lentulus and Lucius Manlius Acidinus were sent there with proconsular power "without magistracy" ("sine magistratus", without holding public office). Neither of them had been a consul before. Therefore, they were sent to Hispania without having held consular public office, but they were given proconsular power so that they could command armies there. This was a constitutional oddity. It gave the Roman territory in Hispania a somewhat unofficial status. This situation continued until 198 BC when it was decided to create two new provinces: Hispania Citerior and Hispania Ulterior (they were instituted in 197 BC). In 77 BC Pompey the Great was sent to Hispania to support Quintus Caecilius Metellus Pius to fight against Quintus Sertorius in the Sertorian War (80–72 BC). For this purpose the senate gave him proconsular imperium even through he had never been a consul.
The term provincia referred to a field of responsibility, rather than a geographical administrative area. For example, the judicial responsibility of the urban praetor, who was a chief justice, was called provincia. The term often applied to military responsibility and was used to refer to the areas of military responsibility assigned to the consuls to deal with rebellions or threats of invasions; in other words, the area where imperium was exercised. It was in the Late Republic that the term provincia also referred to an administrative area outside Italy. When provinces in the modern sense of the word were established, they were originally the areas where the promagistrates exercised their military power. These governors performed judicial roles in arbitrating disputes between Romans and locals and between the local themselves. They gave the final pronouncements in cases where the laws of the locals did not apply or when there was an appeal. The foundation of this was the governor's ability to enforce his rulings through his military power. In theory, the Senate was meant to supervise the governors, but the distance of many provinces from Rome made this impracticable.
Like the magistrates, the promagistrates were accountable for their actions while in office and liable to prosecution after their term of office was over. However, prosecution would occur post facto and there was a reluctance to convict members of the elites. Impunity was the general rule. Alternatively, the defendants could go into self-imposed exile in other cities to escape punishment. In 171 BC envoys from the provinces of Hispania Citerior and Hispania Ulterior presented complaints about extortion against three former propreaetors in the two provinces. They were put on trial. The trial of one of them was adjourned twice and on the third session he was acquitted. The other two cases were also adjourned and the other two men went into exile outside Roman territory before the new trial. One of the charges was unjust valuation of grain received as tribute. The senate decreed that no Roman official was to be allowed to set the price of grain or force the locals to sell the levied 5% quota at the price he wished. The senate appointed the recuperatores (recuperators) to investigate extortion and maladministration by the propraetors and to recover damages for provincial plaintiffs. In 149 BC the Calpurnian Law established the standing court of recovery of property (quaestio de pecuniis repetundis) which was instituted to deal with cases of extortion. The lex de rebus repetundis passed by Gaius Gracchus in 133 BC transferred the judges of these courts from the senatorial order (from which the promagistrates were drawn) to the equestrian order. This was the main means by which the provincials could prosecute former governors. If an ex governor was found guilty, he would have to restore twice the value of what he had misappropriated and face disgrace. However, such persecutions were to be undertaken in Rome and it was expensive for provincials to travel there and stay there. Moreover, there still was the possibility of the accused leaving Rome to escape prosecution. Verres, who had been governor in Sicily between 73 and 70 BC, was prosecuted by Cicero when he returned to Rome for maladministration, fraud and extortion. When he realised that he stood no chance of acquittal, he fled to Marseilles, where he lived off the money he misappropriated in Sicily.
The quaestors also served in a provincial administration. When a quaestor died in his province, the governors appointed a proquaestor in his stead. In Rome the quaestors were the treasurers. In the provinces they were in charge of the finances of the province. Originally there were only two quaestors who supervised the aerarium in Rome. In 421 BC their number was doubled. From then on when the consuls undertook a military campaign they were accompanied by one quaestor each. The quaestors who remained in Rome came to be called quaestores urbani. Initially the role of these travelling quaestors was to oversee the sale of the war booty, part of which was given to the troops and part of which was given to the aerarium. Later they kept the treasury's fund from the army and gave the soldiers their pay. In 265 BC the number of quaestors was increased to eight. One quaestor became the quaestor ostiensis. He was based at Ostia, Rome's port, and was in charge of the grain provisions for the city. Three other quaestors were sent to towns in Italy to raise those parts of the revenue which were not farmed by the publicani (see below) and to control them. Two were sent to Sicily. Lucius Cornelius Sulla increased their number to twenty and Julius Caesar to forty. The quaestors who were seconded to the proconsuls or propraetors in the provinces most probably performed the same functions as those who accompanied the consuls on their campaigns. An important part of their role was paying the soldiers and procuring provisions for the army. Like the quaestors in Italian cities, they also levied those parts of the public revenue in the province which were not farmed by the publicani controlled them. They had to send the raised revenues and their account to the aerarium. When the governor was absent from the province the quaestor took his place in an acting capacity and was then attended by lictors. The quaestor in the provinces also performed the duties of the curule aedile. The relationship between governor and quaestor was according to ancient custom regarded as resembling that between a father and his son. Sicily, the first Roman province, had two quaestors owing to the presence of Carthaginian and Greek territories when it was annexed. One was based in Syracuse and one in Lilybaeum. In the period of rule by emperors the quaestors continued to serve in the senatorial provinces. In the imperial provinces they were replaced by the procuratores Augusti (see below).
In 27 BC, when Augustus established rule by emperors, the provinces of the Roman Empire were divided into imperial provinces and senatorial provinces. Augustus professed that the senate would keep the finest portion of the empire while he would take on the hardship and danger of defending precarious provinces which were vulnerable to internal rebellions or to external attacks (in the case of provinces along the borders of the empire). In reality he kept the provinces where the bulk of the legions were stationed and left the senators provinces which would be unarmed and unprepared for battle. Among the senatorial provinces, Asia and Africa were assigned to ex-consuls, and the others to ex-praetors. It was established that only this class of senators could pronounce a death sentence. The propaetors chose their provincial assessors from their peers or from their inferiors. The proconsuls chose three assessors form those of equal rank, subject to the emperor's approval. In the imperial provinces which had more than one legion, the governors, the legati Augusti pro praetore, were lieutenants of the emperor appointed by him and were usually propraetors, although sometimes they were ex-quaestors or men who had held other offices below the praetorship. With the propraetors in the imperial provinces being subordinates of the emperor, the latter could exercise better control over the administration of their governors. Many of the letters written by Pliny the Younger have survived. Book 10 of this collection contains the correspondence he had with the emperor Trajan during his governorship in Bithynia et Pontus in 110–113. In these letters Pliny informed the emperor about affairs in his province and often asked for instructions on specific matters. Trajan provided them in his replies.
During the period of the Roman Republic tax collection was tendered to private companies owned by the publicani (singular publicanus). These extracted money form the provincials unscrupulously to line their pockets. Livy wrote: "wherever there is a publicanus either public law is disregarded or the liberty of the allies is reduced to nothing."  Julius Caesar abolished this system of tax collection and restored the custom of assigning this task to the cities in the provinces. Augustus handed this task to his own officials. In the imperial provinces the quaestors were replaced by the procuratores Augusti (imperial procurators) as the chief financial officers, who took direct charge of financial matters, including tax collection. These financial procurators were appointed by the emperor and were the agents of the emperor. The term procurator originally applied to agents, especially those who went away for Rome for some time on state business. They were direct subordinates of the emperor and therefore worked independently from the governors. They were responsible for the collection of rent in the imperial estates (Augustus has acquired large amounts of land from previous local rulers and potentates), tax collection, the supervision of mines and from paying civil servants and the soldiers. Thus, the financial system operated as an independent executive system. Good collaboration between legati Augusti pro praetore and procurators was advisable as the latter were the paymasters to the army. The building of fortifications was also supervised by the procurators. They belonged to the equestrian order or were freedmen who had been imperial slaves and thus they were not connected with the senatorial order. With the procurators the emperors gained direct control over finances in the imperial province. These men were also a source of independent information for the emperor. There were also procurators in the senatorial provinces to supervise the imperial estates in those provinces as well.
Tacitus wrote that Augustus conferred judicial power to the equestrian governors of the province of Egypt and that later a large number of judicial cases which had been presided over by the praetors both in Rome and in the other provinces were similarly transferred. The emperor Claudius (reigned 41–54) remarked that the judgement of his procurators ought to have the same validity as the rulings of the emperor and handed the judicial power over to them in full. In this manner the emperor gained direct control over judicial matters via their procuratorial agents in Rome. The role of the praetors in Rome was reduced to organising public games. With regard to the provinces, Tacitus did not specify whether this applied to both imperial and senatorial provinces. He did not use the term propraetor either. Given that in the senatorial provinces the role of the procurators was restricted to supervising the imperial estates, it is unlikely that they took on judicial roles there. The mentioned correspondence between Pliny the Younger and Trajan, who reigned later (98–117), indicates that the governor of Bithynia et Pontus, a senatorial province, did preside over judicial cases. In 359 AD Constantius II (the son of Constantine the Great) tried to revive the old judicial role of the praetors in Constantinople by assigning cases regarding guardianship, the emancipation of sons from the legal authority of their fathers (patria potestas) and the manumission of slaves to them.
Procurators were also appointed as governors of small provinces. Under Augustus and Tiberius they were called praefecti (singular praefectus).
The power of a promagistrate in the Roman provinces has led to the term proconsul being used to designate any high-ranking and authoritative official appointed from above (or from without) to govern a territory without regard for local political institutions (i.e., one who is not elected and whose authority supersedes that of local officials). One of the most prominent examples of this is Douglas MacArthur, who was given vast powers to implement reform and recovery efforts in Japan after World War II, and has been described occasionally as "the American proconsul of Japan".
On their appointment, nuncios are also appointed bishops. In the time of Pope Pius XII, some priests were appointed Nuncios without being raised to the status of bishop. They were not called "pro-nuncios", a title that historically was given to nuncios from the moment their appointment as cardinals was announced until their departure for Rome, and that was revived for some twenty years (ending in 1991) as a distinct title for nuncios accredited to those countries that did not follow the tradition of considering the nuncio as Dean of the Diplomatic Corps from the moment he presented his credentials.