This chapter will explore the significance and impact of the Roman military as one of the central institutions of the Roman Empire through its material legacies from the Late Republic to the early fourth century. Studies of features and finds from frontier installations, camps, fortresses, and the settlements and cemeteries surrounding them, as well as military equipment and images on monuments, provide insights unobtainable from literary sources. They illuminate the multifarous role of the military in the development of the empire: its social, political, and economic networks, mentalities, values, norms, and needs; relations within the military and among military units; and the dynamic, multifaceted relationships between military and civilian populations in Rome and its provinces. The archaeology of the Roman military thus contributes to a better understanding of essential developments and interconnections in the Roman Empire, without forgetting that the military functioned as an instrument of conquest and subjugation.