Between the late second and the early fourth century CE, several empresses received the title Mater Castrorum, either in official documents, inscriptions, and coinage or in unofficial honorific or dedicatory inscriptions erected by subjects. Scholars have assumed the title was indicative of a tight-knit relationship between the empresses and the soldiers. Recent studies of the numismatic and epigraphic evidence, however, have demonstrated that, at least in the cases of the early Matres Castrorum, the title was not descriptive of an actual relationship with the military. These studies argue it was the product of dynastic propaganda that prepared a smooth path for successors. Given this new, demonstrated understanding of the title’s original purpose this chapter investigates how the title fits into ideologies that emperors “negotiated” with the constituencies in the Empire. Based on the evidence, we conclude that the meaning and use of the Mater Castrorum title changed over time according to the agenda of those who employed it. The evolution of the title is not surprising, but as with so many aspects of investigations into women and the military, the complexities of its use have not previously been conceived of in this way.