The present paper deals with one of the little-studied issue of the Late Roman military history during the time of Tetrarchy (284-305 A.D.), that is a role, functions and status of the prominent legio III Augusta established as early as during the Early Empire and located in North Africa, in the province of Numidia. The author stud- ies this point by the example of military campaign of Emperor Maximianus Herculius, who ruled over western provinces of Roman Empire during the time of Tetrarchy. This campaign was held against the tribes of the Moors in the North Africa. Maximianus managed this campaign in 297/298. Previous scholarship constantly argued that in the frameworks of this campaign Maximianus commanded military units (the so-called vexilla- tions) detached from the staff of Rhine and Danubian legions, i.e. legions which served beyond the North Afri- ca. Based on a series of inscriptions and hagiographic sources, the author proposes that the local legio III Au- gusta also took an intensive part in battles with the Moors, this legion was involved in the campaign because of its territorial location, i.e. the legion stood in Numidia, which was very close to the regions of fighting. The author traces and reveals the internal structure of vexillation. The mechanism of its establishment and peculiar- ities of its regular staff are defined.