The Arcani or Areani were a Roman paramilitary group which acted as a secret police force for the state. 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. The Arcani were mostly tasked with reconnaissance duties and intelligence missions around the frontiers, giving detailed reports about enemy forces and leaders. The majority of them most likely had military experience, especially “field agents”, whose mission it was to infiltrate enemy territory. We don’t know much about their techniques of 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. They may have worked alongside the Exploratores and Praeventores in supervising the frontier. 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, particularly in regards to the Great Conspiracy, a joint invasion of Britain which included the Attacotti, the Franks, the Saxons and the Picts, the Arcani were disbanded by Count Theodosius the elder, father of future emperor Theodosius I. The Arcani were, and continue to be, often subject of romanticized depictions and wild speculation, especially because very little is known about them. Perhaps the mystery surrounding the Arcani was meant from the beginning?