Mounted Praetorian wearing a masked helmet usually used in the hippica gymnasia.

In Roman times, intelligence activities were performed by various units whose functions often overlapped. Originally, the Frumentarii, Beneficiarii,  Speculatores and Exploratores were specialized body of troops who provided supplies to the Roman legions and gave them detailed reports about enemy forces. In Imperial times, particularly during the reign of emperor Hadrian, these units gradually became part of a secret service body who loyally served the Princeps. These elite troops were headquartered in the Castra Peregrina on the Mons Caelius in Rome and operated under the command of the Princeps Peregrinorum, a powerful officer responsible for the security of the roman State who answered directly to the emperor.

As displayed on the low reliefs of the Trajan’s Column in Rome, the Frumentarii were, in origin, concerned with the supply of frumentum or corn to the Roman legions. They acted as internal secret police, couriers and security enforcers, carrying out undercover activities both in Rome and in the provinces. We have evidence of collaboration between the Frumentarii and the Cohors Praetoriae or Praetorians in police and security operations in Rome. Most probably, during the 3rd century AD crisis, the Frumentarii played a crucial role in breaching the personal security of emperors, as they had a privileged connection to the Praetorian Guard.

The Speculatores gathered information on Rome’s external enemies and functioned as elite reconnaissance units, messengers and collectors of intellingence. At times, they also acted as assassins and torturers on behalf of the emperor. However, the use of Speculatores was not limited to the Princeps. Provincial guards also employed them for similar purposes. Evidence shows that Speculatores often operated alone, in pairs or small groups and were executed if captured. The Speculatores operated alongside of the Cohors Praetoriae in Rome, in particular of the Equites  Singulares Augusti, the cavalry arm of the Praetorian Guard, and were led by a Centurio Speculatorum Augustorum, a powerful Praetorian officer. The Praetorian Guard or Cohors Praetoriae, were used by emperors as means of terror tactics, assassination and gathering of intelligence, similarly to the Frumentarii. The Speculatores continued to be employed throughout the empire.

The Exploratores were a trained scouting unit to be found in every roman legio. They were sent forward in screening operations and reconnaissance missions, providing excellent situational awareness to roman legions. As evidence from the panels of the Trajan’s Column in Rome shows, they were given first-class horses and equipment in order to increase their mobility when carrying out combat intelligence missions behind enemy lines such as raids, attacks on enemy outposts and foraging operations.

To conclude, the Beneficiarii were specialized soldiers who served under military commanders and governors and had administrative and logistical tasks. At times, even diplomats and courtiers were sent off to foreign courts to spy on enemy kings or rival emperors.

The Frumentarii, Beneficiarii, Speculatores and Exploratores were heavily involved in the violent persecutions of Christians and were most probably the ones who carried out assassinations and tortures.