This book investigates the structural, cultural, and military significance of the Roman Auxilia, the non-citizen forces that comprised over half of the Roman imperial army. Ian P. Haynes, a specialist in Roman military history, utilizes archaeological evidence, epigraphic data, and historical records to reconstruct the lives of these soldiers. He argues that the Auxilia were not merely auxiliary support but were fundamental to the expansion, administration, and maintenance of the Pax Romana across the diverse provinces of the empire.

Scholars and historians recognize this work as a definitive reference for understanding the composition of the Roman military machine. Readers frequently note the academic density of the prose, which provides a rigorous examination of the auxiliary forces for both students and researchers of the ancient world.