The Late Roman period saw a series of different intelligence gathering agencies, both civilian and military, undertake a myriad of tasks for the Roman state, often overlapping with one another. After the centralization of state power by the Illyrian emperors during the 3rd century AD, the Roman system of gathering intelligence within the empire underwent a series of reforms. An increasingly centralized government led to more coercion, harsher laws, as well as more organized groups for intelligence gathering and internal espionage. The old imperial frumentarii, military men involved in various intelligence gathering activities, were disbanded by Emperor Diocletian, who replaced them with the schola (corporation) of the agentes in rebus, literally “those involved in matters”, imperial couriers between the court and the provinces who also served as domestic intelligence officers reporting directly to the emperor.
Different from the frumentarii, the agentes in rebus were civil servants enlisted as soldiers and organized similarly to non-commissioned officers in the Roman army. It is believed that most agentes were not of high social status and are described by philosopher Libanius as often wearing typical Germanic military pants (bracae) which, in his eyes, made them look foreign and barbarian. Similarly to the defunct praetorian guard, candidates needed recommendation letters to attest their moral integrity and good character. As seen in his letters, Libanius once wrote a recommendation for one of his friends in order for him to be recruited as an agens. Even though the exact size of the agentes varies from one period to another, it is believed that they were much more numerous than the frumentarii, their number reaching 1,174 in the year 430 AD according to the Codex Theodosianus. Unlike modern-day intelligence agents, Late Roman agentes in rebus did not work in the shadows but operated openly as declared imperial agents. Their generic name is meant to obfuscate the exact nature of the varied intelligence activities they performed. Their duties included carrying out special operations such as the arrest of political opponents, providing additional muscle to regional tax collectors, transmitting important information to the imperial court and investigating criminal matters regarding the cursus publicus, the imperial postal system. Agentes were also employed by emperors as informers and mediators in factional religious contrasts and persecutions. Eastern emperor Valens sent agentes to the city of Casarea, modern day Turkey, in order to mediate between Nicene and Arian factions in the city.
The growth of bureaucracy in the late Empire created another use for both the agentes in rebus and the notarii (imperial secretaries): control of certain ministries of state. As a matter of fact, both the agentes in rebus and the notarii were seconded as chiefs of staff or adiutores (assistants) of high-ranking officials such as praetorian prefects, correctores and vicarii so that the central government was able to keep an eye on local administrators and obtain information whenever needed. Nonetheless, instead of spying on their superiors, they often ended up engaging in criminal activities together, hoping to receive help for their careers. Therefore, the agentes in rebus were prone to political corruption, blackmailing public officials to avoid public prosecution or manipulating public or court opinion to favour imperial opponents. Their corruption is proved by the public execution by Emperor Valentinian I of several agentes accused of treason and embezzlement. The influence they were able to exercise on the imperial court is shown by the fact that, according to the Codex Justinianus, they could not be prosecuted, not even by the emperor himself, unless the magister officiorum, head of the court office, gave his permission. Their prosecution by Valentinian was therefore illegal, and constituted an attack on the agentes.
In addition to the agentes in rebus, the schola notariorum also acted as a domestic intelligence force for the state. At face value, the notarii were bureaucratic secretaries for magistrates, courtiers and military personnel. However, the schola notariorum, cenetered around the imperial court, was particularly involved in documentary investigations such as handwriting tests and in regulating the flow of information in the provincial governments. They were led by the primicerius notariorum, an influential figure. An example of a prominent imperial notarius is Paulus, nicknamed Catena (chain), an agent of Emperor Constantius II, well-known for his infamous investigations on the remaining supporters of the usurper Magnentius, who was burned alive by Emperor Julian, an enemy of Constantius II.
A more clandestine and specialised role, particularly in domestic affairs, was played by the curiosi, a relatively small subgroup of the agentes in rebus. Most probably, the curiosi were selected by the Master of Offices based on rank and seniority. Their duties included gathering information on individuals the emperor wanted to monitor without his court becoming aware. The curiosi also acted as imperial investigators and inspectors regarding shipwrecks and murders, especially when these occurred on the imperial roads of the cursus publicus, which were essential for the flow of information in the empire. It is likely that the curiosi worked in cooperation with the milites stationarii, soldiers posted in military stationes commanded by regionarii (centurions).
Finding evidence against political opponents whom the emperor wanted to convict was another popular intelligence gathering activity in the Late Roman Empire, which often included fabricating evidence against political opponents. The viatores or messengers, members of the class of the apparitores and assistants to Roman public magistrates, were often involved in criminal investigations, especially those regarding crimes like high-treason or adultery.
Acting as a paramilitary intelligence force for the state were the arcani or areani, a group primarily tasked with reconnaissance duties and intelligence missions around the frontiers, though they were also involved in domestic affairs. Their name means “the hidden ones” or “the secret ones” in Latin, which in and of itself, suggest a role of secrecy. The lack of information about the arcani is another confirmation of their secretive role. Most of the arcani are likely to have had military experience, probably in reconnaissance units such as the praeventores and insidiatores. We don’t know much about their techniques for subterfuge, but most of their covert operations probably took place during diplomatic gatherings, military expeditions or hostage exchanges. During the late Roman period, they were probably responsible for multiple assassinations of foreign chieftains and kings.
According to late Roman author and military officer, Ammianus Marcellinus, by the second half of the 4th century AD, the arcani had become an old and corrupt institution. After being accused of collaborating with the enemy during the Great Conspiracy, a joint invasion of Britain which had to have had significant aid from the inside according to Ammianus, the arcani were disbanded by Count Theodosius the Elder, father of future Emperor Theodosius I.
The quaestor sacri palatii, the chief legal counsellor of the emperor, also had investigative duties in matters relating to the illicit use of magic and court plots. Pannonian quaestor Viventius investigated the illness of the two brother Emperors Valentinian I and Valens, rumored to be the result of the use of magic. Eastern Roman quaestor Fortunatianus investigated rumors of a court conspiracy against Emperor Valens which involved aristocratic members and soothsayers. This investigative function may come from the old role of the quaestores parricidii, public functionaries from the roman monarchy who investigated capital crimes.
However corrupt they may have been, the agentes in rebus managed to retain their role in the Ostrogothic kingdom of Italy, with new Romanized gothic elements. The Late Roman court was a treacherous place, as different factions competed for dominance. Therefore, the security of the court and the chambers of the emperor were ensured by both the candidati and the silentiarii.
The candidati were a regiment of forty members of the scholae palatinae, the imperial guard, selected on the basis of their physical prowess and loyalty to the emperor. The silentiari were high ranking courtiers who kept the chambers of the palatium in check through intelligence gathering and oversight of the candidati. The silentiari were also responsible for the order and summoning of the imperial council, the concistorium, a reunion of the most important members of the imperial elite. Anastatius I, before becoming emperor in 491 AD, was a silentiarius.
To sum up domestic intelligence forces in the Late Roman Empire, it is clear to see that these groups were more numerous than their principate predecessors, even though the were not organized into a single institution or as specialized as modern intelligence agencies. The Late Roman and Early Byzantine central governments improved the intelligence gathering system of their respective empires in direct response to the growing need to exert more control and influence over imperial functionaries and deputies. Corruption was an endemic problem in the Late Roman administration, and also impacted the groups involved in domestic intelligence gathering. This is not to say that the system of domestic intelligence gathering in the empire was weak, as the Late Roman system of agents remained standing in both the Ostrogothic kingdom and the Eastern Roman Empire. Most of our sources demonize these operatives, but, even though we have limited information on them, we can say that they were relatively efficient in their duties, contributing to the longevity of the Eastern Roman Empire.