This paper discusses initial results of a project revisiting archival excavation records of Bu Njem in order to improve the understanding of the role of Roman military garrisons in the pre-desert. Much research on the archaeology of Bu Njem considers the site in separation from the content of its military documentation (ostraca), focusing on the morphology of the fort on the one hand, and the composition of the garrison on the other hand, as a result leaving open the opportunity to study the garrison as an extended military community in its interconnected social, cultural and economic settings. Furthermore, since the completion of fieldwork led by Prof Rebuffat between 1967 and 1980, there have been significant advances to the research on the Garamantes, the understanding of trade in the Sahara and the nature of Rome’s North African frontiers. These advances enable bringing up to date the interpretation of the evidence from Bu Njem. The paper focuses on the archaeology of the principia building as the most extensively excavated structure on the site. Building on existing research, the results add texture to our interpretation of the activities in the garrison and in doing so, the understanding of micro-scale social processes on the frontier.