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Rome's 'Secret Agents'

Updated: Feb 17

There is a tendency to attribute modern structures, ranks and roles to descriptions of the ancient Roman army (Latin: exercitus). Such endeavours are precarious because, despite the seemingly obvious parallels, there is no certain equivalence. That said, today's statecraft requires intelligence to determine the potential threats to a nation so, unsurprisingly, was the case for the Roman Empire. It follows that, given Rome’s highly organised military and civil bureaucracy, the army provided the means to gather the necessary information.

In the early twentieth century, the military intelligence departments of the UK’s War Office (now the Ministry of Defence (MoD)) became the Security Service (MI5), the Secret Intelligence Service (SIS/MI6) and the Government Communications Headquarters (GCHQ). Predictably the functions of these latter day secret organisations can be found rooted in the Roman Empire where internal and external security was as paramount then as it is now. Rome’s intelligence units were created, evolved, and disbanded over the centuries such that, in their long history, they have been known by many names. What follows is an attempt to unravel the ‘who’s who’ and discover what roles, tasks, and functions Rome’s ‘secret agents’ performed.

Firstly, the Romans did not have a formal intelligence service(s) as we understand it today. The reluctance to develop such organisations stemmed from the unique way its republican government had developed. The Roman Senate, which was composed of men from wealthy, upper-class families, acted with a certain amount of class loyalty that allowed the state to push its interests and expand overseas. But the Senate was not of one mind. There was always tremendous personal competition among individuals and families for the wealth and glory that such conquest created. To further their parochial ends, these men needed to know what others were doing and planning, and so they used their private intelligence networks to advance their own careers (Howard, 2006).

The Romans had no qualms about using espionage on a personal level. Every Roman aristocrat had his private network of business associates, informers, clansmen, slaves, or agents (male or female) who could keep him informed on the latest happenings in the Senate, the activities of rival families, or the goings-on in his own home.

Informatores On the Ides of March (March 15th) in 44 BC, during a meeting of the Senate at the temporary Curia in the Theatre of Pompey in Rome, the Roman dictator, Gaius Julius Caesar, was murdered by a group of senators opposed to his dictatorship. When Caesar’s adopted heir Octavianus was elevated to imperial power he was cognizant with the threat of assassination. Known by the title ‘Augustus’, the new emperor was fully aware that the most likely conspirators would be from the upper echelons of Roman society, from the equestrian or senatorial classes. With this in mind, undercover informers, informatores, who were generally chosen from the Praetorian Guard either at the rank of centurion or tribune, were tasked with arresting anyone plotting against the Emperor. To uncover such plots necessitated informatores to operate at the higher levels of Rome’s bureaucracy often requiring them to develop contacts or co-operate with state-level procurators.

Provocatores Much like the informatores already mentioned, provocatores were also tasked with identifying disloyalty toward the Emperor. They operated undercover within Roman territory aiming to gain the trust of those they were investigating. Having done so it is believed provocatores would provoke the intended target (hence the name), for example, to speak ill of the Emperor. Should the target follow the provocator's lead, then said individual would have effectively entrapped themselves and be arrested.

Exploratores As their names implies (exploratio means ‘to explore, to investigate, to examine’), exploratores were the scouts of the Roman army. In the early years of the Principate soldiers selected from the auxiliary cavalry were detached from their units for a length of time for this purpose. We know little, however, about how the exploratores were organised but if they were drawn largely from the cavalry, then the smallest operational unit probably would be a turma consisting of thirty horsemen commanded by a decurion. Although relatively small, these mounted patrols had the flexibility to range far and wide reconnoitring ahead and to the flanks of the legion’s main body to detect the enemy. It is worth remembering that while each turma could protect itself, exploratores were not intended to engage with an enemy force but rather to gather information and report back on its location, strength, activity and direction of movement.

As part of their mission, exploratores also reconnoitred the terrain to identify landmarks or locate obstacles that might hinder or slow a legion’s advance. The latter might include forests or woodland, mountainous ridges and valleys, rivers or wetlands. In doing so, their task would most probably also involve identifying possible crossing points. One final task each day would be to locate a favourable site for the construction of the legion’s marching camp.

It seems exploratores were very much the tactical reconnaissance units of the Roman army. The information they gathered would have informed the legion’s commanders of the immediate intelligence picture while on campaign. At the operational or strategic level, however, information was also needed to protect the empire’s interests, identify unrest in its far-flung provinces, and any external threats posed to its borders. Enter the frumentarii.

Frumentarii On the face of it, frumentarii were ‘grain collectors’ - frumentum, after all, means ‘grain’. Working for the military commissariat they were tasked with ensuring the Army was reliably supplied with this staple of the Mediterranean diet.

There are two main sources of information about the frumentarii, inscriptions on gravestones and anecdotes where the actions of individual frumentarii are mentioned by historians. From inscriptions, albeit except for few named centurions (centurio frumentarius), it seems clear that the frumentarii were mostly attached to individual legions. This strongly supports the idea that their main function was, as their name suggests, to service those legions with grain supplies. These duties would have necessarily involved a lot of travelling and brought the frumentarii into contact with enough locals and natives to acquire considerable information about any given territory. Knowledge of the geography, landmarks, communication routes, and strategic objectives such as settlements, farms or granaries would have been valuable military intelligence.

With the frumentarii ranging far and wide, it seems probable that, in the 2nd-century AD, Emperor Trajan added the role of couriers charged with the conveyance of military dispatches to their tasks. By the time Emperor Hadrian succeeded to the throne, the need for an empire-wide intelligence service had become clear. Yet establishing and funding a new service tasked with secretly spying on the Empire’s citizens was not as straightforward as it might seem. Envisioning the large scale of the operation, Hadrian followed his predecessor’s example and turned to his ‘private agents’ - presumably the frumentarii - to be a ready-made information gathering service and couriers of official messages.

In The Life of Commodus it is reported that the emperor’s Praetorian prefects had a particular individual, who was felt to exert a negative influence over the emperor, ‘assassinated by means of their private agents’ (Historia Augusta, The Life of Commodus, 4.5). Once again the use of the term ‘private agents’ may allude to the clandestine activities of the frumentarii.

It seems that the duties of the frumentarii evolved over time, developing from their initial connection with the grain supply and the necessity to travel between Rome and its provinces. Although each frumentarius appears to have belonged to a particular legion, they seem to have liaised with a central bureaucracy in the Castra Peregrina (‘camp of the foreigners’). Their freedom of movement no doubt led to their employment throughout the second century as couriers and messengers. The clandestine nature of the frumentarii‘s tasks may have been exploited so that, on occasion, they may have acted as imperial assassins. but more often than not they represented the forces of law and order.

Speculatores In both the legions and in the praetorian camp, speculatores were initially scouts tasked with gathering as much information as possible about the enemy. It should be fairly evident, therefore, that what was collected by speculatores and the more numerous exploratores (see above) often overlapped.

Over time, however, it seems speculatores became imperial bodyguards, couriers, law-enforcers, and sometimes executioners. Where such tasks required the wearing of ‘plain clothes’ may explain why they were considered ‘spies’ (Occulta speculator / speculatrix). Units were organised in the standard legion manner led by a centurion and his ‘chosen man’ or Optio, and commanded by the Centurio Speculatorum Augustorum when accompanying the emperor on military campaigns.

On the suicide of Emperor Nero, the first permanent imperial bodyguards, the Corporis Custodes (also known as Germanic or Batavian bodyguards), were replaced by the new Emperor Galba’s own bodyguard, the speculatores. They remained the imperial bodyguard until the Emperor Trajan promoted his own Equites Singulares to the role.

Despite being the emperor’s private, standalone unit, complete with its own barracks, the speculatores were frequently counted part of the Praetorian Guard. Indeed, it seems the Guard, especially its cavalry element, was a prime recruiting ground for speculatores.

Ammianus Marcellinus, a Roman historian, reports that in AD 365 the usurper Procopius sent speculatores to Constantinople to spread hostile rumours about Emperor Valentinian I. If true, then the whispering campaign was somewhat successful as Procopius was elected emperor on September 28th, AD 365, reigning a whole eight months until May 27th, AD 366.

Arcani Vindolanda Tablet 162, pictured, is a fragment of a leaf containing two words, ‘miles arcanvs’ written in a good capital hand. The Roman Inscriptions in Britain (RIB) website suggests it is possibly some sort of ‘tag’, merely recording the name of a Roman soldier since ‘Arcanus’ is a known cognomen [1]. Alternatively, it might be a reference to some type of intelligence officer or agent (see exploratores above). In the latter context, the only reference to arcanus is by Ammianus Marcellinus (Book 28.3.8):

‘...haec etiam praecipua arcanos [2] genus hominum a veteribus institutum, super quibus aliqua in actibus Constantis rettulimus, paulatim prolapsos in vitia a stationibus suis removit: aperte convictos, acceptarum promissarumque magnitudine praedarum allectos, quae apud nos agebantur, aliquotiens barbaris prodidisse. id enim illis erat officium, ut ultro citroque [per longa spatia] discurrentes, vicinarum gentium strepitus nostris ducibus intimarent...

‘During these outstanding events the arcani, who had gradually become corrupt, were removed by him [Theodosius] from their positions. This was an organisation founded in early times, of which I have already said something in the history of Constans. It was clearly proved against them that they had been bribed with quantities of plunder, or promises of it, to reveal to the enemy from time to time what was happening on our side. Their official duty was to range backwards and forwards over long distances with information for our generals about disturbances among neighbouring nations.’

Ammianus’ description implies the arcani were a longstanding institution and appear to have been a force based in Britannia during the later period of Roman occupation of the island. They had played some part in the campaign of Constans in Britain in AD 343 and later helped to instigate the Great Conspiracy in AD 367 - 368 [3]. Due to their participation in the Conspiracy, Count Theodosius disbanded them (Marcellinus, Book 28.3.8) [4].

The duties that Ammianus describes, traveling and reporting the news of the tribes to Roman leaders, are appropriate to military scouts (Richmond, 1958, 115). It is conceivable that the arcani may have lived and operated in the paramilitary zone between the Antonine Wall running across Caledonia (Scotland) and the Vallum to its South. It is tempting to speculate that the Vindolanda tablet might be an ‘identity card’ carried by someone moving about the countryside, conducting reconnaissance in ‘plain clothes’, which could be produced if challenged by other Roman military personnel? It is not beyond the realms of possibility, but we cannot know for certain.

Agentes in rebus The agentes in rebus were the late Roman imperial courier service and general agents of the central government from the 4th- to the 7th-centuries AD. The exact date of their institution is unknown. They are first mentioned in AD 319, but may date to Diocletian's reforms in the late 3rd-century when they replaced the earlier and much detested frumentarii (see above) The central imperial administration still needed couriers, however, and the agentes in rebus seemingly filled this role.

Their title translates as ‘Those Active in Matters’, an ambiguous description that may hint at the multiplicity of tasks they may have been called upon to perform. Originally operating as dispatch carriers, they eventually assumed a variety of duties under the jurisdiction of the magister officiorum (Master of the Offices). The organisation survived into the Byzantine Empire, being eventually abolished sometime in the early 8th-century AD, as most of the magister's functions were taken over by the logothetēs tou dromou (Kazhdan, 1991, pp. 36-37).

The agentes in rebus were formed into a militarised schola (‘imperial guard unit’) of the palace in common with other public services of the Dominate. As a militia, the five ranks of agentes were derived from those of junior cavalry officers of the late Roman army: equites, circitores, biarchi, centenarii and ducenarii (Kelly, 2004, 20, 40). Two were appointed to each province in AD 357, one in AD 395 and more again after AD 412. According to Codex Justinianeus (the Code of Justinian, XII.20.4) the agentes enjoyed immunity from prosecution in both the civil and criminal courts, unless otherwise sanctioned by the Master of Offices. Senior agentes were regularly appointed to the post of princeps officii (the ‘chief of staff’ or ‘permanent secretary’) of the praetorian prefectures, the urban prefectures in Rome, and the dioeceses [5] across the Empire thereby exercising control over these departments' bureaucracy and reducing its independence (Kelly, 2004, 96, 210). As for their function, the 6th-century historian Procopius notes:

‘The earlier Emperors, in order to gain the most speedy information concerning the movements of the enemy in each territory, seditions or unforeseen accidents in individual towns, and the actions of the governors and other officials in all parts of the Empire, and also in order that those who conveyed the yearly tribute might do so without danger or delay, had established a rapid service of public couriers.’ (Procopius, Secret History, XXX)

This is essential the role ascribed to the aforementioned frumentarii, but as couriers their duties included the supervision of the roads and inns of the cursus publicus (public postal system), the carrying of letters, or verifying that a traveller was carrying the correct warrant (evectio) while using the cursus. Further duties assigned to the agentes included the role of customs officers, the supervision of public works and the billeting of soldiers (Kazhdan, 1991, pp. 36-37). They were also used to supervise the arrest of senior officials as required, to escort senior Romans into exile, and even to assist in the enforcement of government regulation of the church (Sinnegan, 1959, 248). Ammianus Marcellinus and Procopius also noted their use as ambassadors on several occasions (Sinnegan, 1959, 249).

Other tasks included supervising the provincial bureaucracy and delivering Imperial commands, often staying in the area to ensure their implementation. Being outside the control of the provincial governors, some agentes, the curiosi, were appointed as inspectors (Kazhdan, 1991, pp. 36-37), for which they gained a reputation for being some form of secret police (Jones & Tomlin, 2015). Yet the vast majority of agentes operated quite openly and thus claims of them actually being a ‘secret police force’ are certainly exaggerated (Kelly, 2004, 207).

Their routine assignments brought agentes into contact with matters of great concern to the imperial court. Given that they reported back to the court on everything they saw or heard on their varied missions, the agentes must have performed an intelligence function in the broadest modern sense of the term (Kazhdan, 1991, pp. 36-37). This role, as well as their extraordinary power, made them feared.

Beneficiarii Most modern armies have hierarchical rank structures, with officers and soldiers typically identified by their rank. Ordinary soldiers, for example, can be ‘privates’ but they also can be ‘Riflemen’, Guardsmen’, ‘Troopers’, ‘Gunners’ and so on. To confuse matters sometimes they can be identified by their specialisation such as ‘Craftsmen’ in the Royal Electrical and Mechanical Engineers (REME), ‘Signaller’ in the Royal Signals, or ‘Drummer’, ‘Trumpeter’, ‘Bugler’, ‘Piper’ and ‘Musician’ in various military bands and other units. Given that the Roman army has tended to be the model for modern armies it is tempting to equate ranks and positions across the centuries. Attempts to align the ranks of the Roman army with its modern descendants is fraught with problems. There are some parallels at the higher levels of command. For example, based purely on the number of soldiers under his command in a legion, namely about 5,000, the Legatus legionem is described by some authors as a ‘Brigadier General’ who today typically commands a brigade of roughly equivalent strength [6][7]. As one descends the rank structure, however, the roles and responsibilities increasingly diverge or simply do not correlate.

With that in mind, beneficiarii (sing. beneficiarius) are often assumed to be ‘officers’ in the Roman army below the rank of centurion but this is not really the case. While the title had existed at least from the time of Caesar, by the imperial period a beneficiarius ranked among the principales (who received pay at one‐and‐a‐half times or twice normal legionary rates) and performed administrative duties. A man was appointed beneficiarius through the favour (beneficium) of their commander usually after serving as an immunis [8], and then holding one or more posts in the century, such as officer in charge of the watch (tesserarius), standard‐bearer (signifer), or orderly. Moreover, the rank of each beneficiarius depended on the status of the official to whose office he was attached. These included procurators, senior military officers (both praefecti of auxiliary cohorts and legati legionis had them), the praetorian prefects, or those most commonly found with the title beneficiarii consularis who worked for provincial governors. Regardless of who’s staff they were attached, beneficiarii performed administrative and legal tasks on behalf of their commander; in effect they acted as his aide-de-camp [9]. Beneficiarii could often expect promotion to the centurionate.

Pictured right is a replica of a distinctive class of iron spearhead with broad shouldered blades excavated in Wiesbaden, Germany. It was made by Len Morgan and is shown carried by the late Juris Trede, both founder members of the Roman Military Research Society (RMRS). Surviving examples of these spears ‘exhibit features such as coper-alloy inlays, silvering, circular or slot perforations, and attached rings’ (Bishop & Coulston, 2006, 152). The one shown is decorated with acorns, one at the finial and two attached as pendants [10]. Such spearheads are found carved on monuments erected by and for beneficiarii, frumentarii, and speculatores. It follows, therefore, that such ‘soldiers presumably carried spears as rank insignia while engaged in specialist administrative, supply and policing duties’ (Bishop & Coulston, 2006, 153) [11].



Ammianus Marcellinus Liber XXVIII III VIII.

Bishop, M.C. & Coulston, J.C.N., (2006), ‘Roman Military Equipment from the Punic Wars to the Fall of Rome’, Oxford: Oxbow Books.

Historia Augusta, ‘The Life of Hadrian’, Loeb Classical Library (1921), Available online (accessed March 30th, 2022).

Historia Augusta, ‘The Life of Commodus', Loeb Classical Library (1921), Available online (accessed March 30th, 2022).

Howard, E., (2006), ‘Espionage in Ancient Rome’,, Available online (accessed June 5th, 2022).

Jones, A.H.M. & Tomlin, R.S.O., (2015), ‘agentes in rebus’, Oxford Research Encyclopedia of Classics.

Kazhdan, A., ed. (1991), ‘Agentes in rebus’, The Oxford Dictionary of Byzantium, Oxford and New York: Oxford University Press.

Kelly, C., (2004), ‘Ruling the later Roman Empire’, Cambridge, MA: Harvard University Press.

Richmond, I. A., (1958), ‘Roman and Native in North Britain’, Chapter V ‘Roman and Native in the Fourth Century’, Nelson, p. 115.

Sinnegen, W.J., (1959), ‘Two Branches of the Roman Secret Service’, The American Journal of Philology, 80 (3), pp. 238–254.

Stevens, C. E., (1955), ‘Hadrian and Hadrian's Wall’, Latomus, Vol. 14, No. 3, pp. 384-403, referenced in Richmond, op cit.


1. Under Roman naming conventions a cognomen was a citizen’s third name. Initially, it was a nickname, but lost that purpose when it became hereditary. Subsequently cognomina were used to augment the person’s second name, their gens, to identify a particular branch within a family or family within a clan.

2. The manuscript reading is areanos, which may be a misspelling in antiquity where the ‘c’ was mistaken for an ‘e’. According to Stevens, the term ‘areani’ means ‘people of the sheep-folds’ (Stevens, 1955, 395), and many of the homesteads in the frontier region were indeed sheep-folds (Richmond, 1958, 115).

3. The Great Conspiracy was a year-long state of war and disorder that occurred in Roman Britain near the end of the Roman rule of the island.

4. Flavius Theodosius (died AD 376), also known as Count Theodosius (Latin: Theodosius comes) or Theodosius the Elder (Latin: Theodosius Major), was comes rei militaris per Britanniarum (Commander of the Troops of the Diocese of the Britons) a senior military officer serving Emperor Valentinian I (r. AD 364 - 375) and the western Roman empire. Under his command the Roman army defeated numerous threats and incursions, including the Great Conspiracy (AD 367 - 368) and the usurpation of Valentinus. Theodosius was patriarch of the imperial Theodosian dynasty (r. AD 379 - 457) and father of the emperor Theodosius the Great (r. AD 379 - 395).

5. The praetorian prefectures were the largest administrative division of the late Roman Empire, above the mid-level dioceses and the low-level provinces. In the Late Roman Empire, regional governance grouped provinces into civil dioceses each headed by a vicarius, the representative of praetorian prefects, who directly governed the diocese in which they resided. There were initially twelve dioceses, rising to fourteen by the end of the 4th-century AD. The urban prefecture had a long history dating back to the time of the kings of Rome. The office of the praefectus urbi was tasked with maintaining order within Rome itself, but its powers also extended to the ports of Ostia and the Portus Romanus, as well as a zone of one hundred Roman miles (c. 140 km) around the city.

6. The rank of Brigadier General first appeared in the British army during the reign of King James II (1685 to 1688). Almost interchangeably since its inception, the British simply called the holder a ‘Brigadier’. A warrant of 1705 placed the grade directly below Major General. Some readers may be confused that the next rank up is a ‘Major General’ followed by a ‘Lieutenant General’, after all a ‘Major’ is two ranks above a ‘Lieutenant’. The explanation is, however, quite simple. Just as the British dropped the ‘general’ in ‘Brigadier General’, by the 18th-century they had also quietly dropped the ‘Sergeant’ in ‘Sergeant Major General’, which had been the most junior of the general ranks.

7. The typical NATO standard brigade consists of approximately 3,200 to 5,500 troops.

8. Immunes were legionary soldiers who possessed specialised skills which excused them from routine labour and guard duties. Engineers, artillerymen, musicians, clerks, quartermasters, drill and weapons instructors, carpenters, hunters, and medical staff were all considered immunes. Regardless, these men were still fully trained legionaries and were called upon to serve in the battle lines when needed.

9. An aide-de-camp is a personal assistant or secretary to a person of high rank, usually a senior military, police or government officer, or to a member of a royal family or a head of state. While still trained soldiers, Beneficiarii were immunes closely associated with a high ranking officer and thus unlikely to be called upon to fight unless in extremis.

10. The acorn appears to have been a symbol associated with fertility and the creation of life. In the iconography of rulers, however, it was a reference to their special relationship with powerful gods, who protected them and allowed them to rule using their divine justice. As the representative of emperors, acorns on the beneficarius’ spear are thus symbolic of imperial power.

11. Several online sources quote beneficarii performing the role of ‘military police’. To imply the Roman army had military police officers or units as we would understand the terms today has not been substantiated by contemporary written or graphic evidence. Bishop and Coulston do mention a ‘policing’ role but it far from certain that beneficiarii were actively maintaining law and order or enforcing regulations or agreements in the sense of a modern police force’s role. So, while beneficiarii were in the military and perhaps policed rules and regulations administratively on behalf of a high ranking officer, it is probably wrong to think of them as ’military police’.


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