This comprehensive work details the auxiliary units of Roman Britain, covering their histories, movements, campaigns, and notable members.

The majority of work on Roman Britain's military focuses on the legions, with much less attention paid to the auxilia, even though the latter formed the vast majority of the manpower. The auxiliary units were drawn from all over the Empire and provided both infantry and cavalry units, many of which provided specialisms that the legions lacked. For example, the Cohors I Hamiorum Sagittariorum were a cohort of archers from Syria stationed at Carvoran fort on Hadrian's Wall.

Simon Turney, following decades of research, presents this work, referencing every one of the fifty-nine auxiliary units identified in Britain. For each there is a unit history, detailing their movements, involvement in campaigns and anything noteworthy. This is followed by a set of lists detailing known, attested members of the unit and any inscriptions that mention them. Each entry is also accompanied by photographs and/or maps, including the sites the unit occupied, tombstones, images, inscriptions and so on. This is the finest, most up-to-date reference available for the auxiliary units of Britain.