The network(s) of Mithraism: discussing the role of the Roman army in the spread of Mithraism and the question of interregional communication

The cause of the rapid and geographically impressive spread of Mithraism in the Roman Empire from the last quarter of the 1st century CE onward is still only partially explained. Scholars had speculated about the influence of the Roman army and the popularity of Mithraism among Roman soldiers; however, a meticulously conducted demographical study of the known followers of Mithras based on Roman epigraphical data problematized this view. This paper uses a transportation network model based on ORBIS (the Stanford Geospatial Network Model of the Roman World) and a network analytical approach to uncover the possible relationship between the network of Roman legionary fortresses and sites where the presence of Mithraism can be historically documented. To demonstrate the possible impacts of Roman military infrastructure on the spread of Mithraism in the Roman Empire, we coded all sites of documented Mithraic presence and the locations of the major Roman legionary fortresses, positioned them on the transportation network, and used statistical analysis to detect possible relationships between these datasets, both at the level of the whole Roman Empire and regionally. Although we were not able to find, at the level of the Roman Empire, a statistically significant overlap between the locations of Roman legionary fortresses and Mithraic sites, we discovered the statistically significant presence of Mithraic evidence in nodes important on thresholded military subnetworks connecting Roman legionary fortresses. These results support the view that the Roman army and supporting civil personnel responsible for supplying and maintaining Roman military infrastructure contributed to the spread of Mithraism and can partially explain the geographical distribution of archaeologically attested Mithraic evidence in the Roman Empire.