Sacramentum militiae : Empty words in an age of chaos

The sacramentum militiae, or military oath of loyalty, has long been recognized as a core component of the relationship between the emperor and the Roman army during the early imperial period.1 Far less, however, is known about its role in the relationship between the emperor and Roman army during the politically volatile period that stretched from the onset of the third century crisis in ad 235 to the death of Theodosius in 395.2 This chapter is an attempt to at least partially rectify this state of affairs. After briefly examining the origins of the sacramentum in the republican epoch this chapter will trace its development through the early imperial period in order to establish a point of contrast for its role from 235–395. It will then establish the basic operation of the sacramentum during this later period, including discerning the content of the oath, the occasions on which it was sworn, and the manner in which it was sworn. These findings will then be used to explain the role the sacramentum played in the ongoing relationship between the emperor and the Roman army.
Here two perspectives will be assessed. The first is that of the emperor. Did he consider the sacramentum to be a tool that could protect him against betrayal by his army? The second is that of the troops themselves. Did they believe that swearing the sacramentum created an actual burden of responsibility to remain loyal to the emperor? And if so, what was the basis of this responsibility and how seriously did they take it?

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