assumed. This is because the 2nd-century auxilia were not just equal in numbers to the legions as in the early 1st century, but some 50% larger. The army of the Principate probably reached a peak of nearly 450,000 (excluding fleets and foederati) at the end of the 2nd century. Furthermore, the evidence is that the actual strength of 2nd-century units was typically much closer to official (c. 85%) than 4th century units. Estimates of the strength of the Army through the imperial period may be summarised as follows: NOTE: Regular land forces only: excludes irregular barbarian foederati units and Roman Navy effectives (40-50,000 during Principate) Army structure The later 4th-century army contained three types of army group: (a) Imperial escort armies (comitatus praesentales). These were ordinarily based near the imperial capitals (Milan in the West, Constantinople in the East), but usually accompanied the emperors on campaign. (b) Diocesan field armies (comitatus). These were based in strategic regions, on or near the frontiers. (c) Border armies (exercitus limitanei). Types (a) and (b) are both frequently defined as "mobile field armies". This is because, unlike the limitanei units, their operations were not confined to a single province. But their strategic role was quite different. The escort armies' primary role was probably to provide the emperor's ultimate insurance against usurpers: the very existence of such a powerful force would deter many potential rivals, and if it did not, the escort army alone was often sufficient to defeat them. Their secondary role was to accompany the emperor on major campaigns such as a foreign war or to repel a large barbarian invasion. The diocesan comitatus, on the other hand, had the task of supporting the border forces of their diocese in major operations. High Command structure East The eastern section of the Notitia is dated to c. 395, at the death of Theodosius I. At this time, according to the Notitia, in the East there were 2 imperial escort armies (comitatus praesentales), each commanded by a magister militum praesentalis, the highest military rank, who reported direct to the emperor. These contained units of mainly palatini grade. In addition, there were 3 diocesan comitatus, in East Illyricum, Thraciae and Oriens dioceses, consisting mostly of comitatenses-grade troops. Each was commanded by a magister militum, who also reported direct to the emperor. The 13 eastern border duces reported to the magister militum of their diocese: (East) Illyricum