Late Roman army
In modern scholarship, the ""late"" period of the Roman army begins with the accession of the Emperor Diocletian in AD 284, and ends in 476 with the deposition of Romulus Augustulus, being roughly coterminous with the Dominate. During the period 395–476, the army of the Roman Empire's western half progressively disintegrated, while its counterpart in the East, known as the East Roman army (or the early Byzantine army) remained largely intact in size and structure until the reign of Justinian I (r. AD 527-565).The Imperial Roman army of the Principate (30 BC-AD 284) underwent a significant transformation as a result of the chaotic 3rd century. Unlike the army of the Principate, the army of the 4th century was heavily dependent on conscription and its soldiers were paid much less than in the 2nd century. Barbarians from outside the empire probably supplied a much larger proportion of the late army's recruits than in the army of the 1st and 2nd centuries, but there is little evidence that this adversely affected the army's performance.Scholarly estimates of the size of the 4th-century army diverge widely, ranging from ca. 400,000 to over one million effectives (i.e. from roughly the same size as the 2nd-century army to 2 or 3 times larger). This is due to fragmentary evidence, unlike the much better-documented 2nd-century army.Under the Tetrarchy, military commands were separated from administrative governorships for the first time, in contrast to the Principate, where provincial governors were also commanders-in-chief of all military forces deployed in their provinces.The main change in structure from the 2nd-century army was the establishment of large escort armies (comitatus praesentales), typically containing 20,000-30,000 top-grade palatini troops. These were normally based near the imperial capitals: (Constantinople in the East, Milan in the West), thus far from the Empire's borders. These armies' primary function was to deter usurpers, and they usually campaigned under the personal command of their emperors. The legions were split up into smaller units comparable in size to the auxiliary regiments of the Principate. Infantry adopted the more protective equipment of the Principate cavalry.The role of cavalry in the late army does not appear to have been greatly enhanced as compared with the army of the Principate. The evidence is that cavalry was much the same proportion of overall army numbers as in the 2nd century and that its tactical role and prestige remained similar. However, the cavalry of the Late Roman army was endowed with greater numbers of specialised units, such as extra-heavy shock cavalry (cataphractii and clibanarii) and mounted archers. During the later 4th century, the cavalry acquired a reputation for incompetence and cowardice for their role in three major battles. In contrast, the infantry retained its traditional reputation for excellence.The 3rd and 4th centuries saw the upgrading of many existing border forts to make them more defensible, as well as the construction of new forts with stronger defenses. The interpretation of this trend has fuelled an ongoing debate whether the army adopted a defence-in-depth strategy or continued the same posture of ""forward defence"" as in the early Principate. Many elements of the late army's defence posture were similar to those associated with forward defence, such as forward location of forts, frequent cross-border operations, and external buffer-zones of allied barbarian tribes. Whatever the defence strategy, it was apparently less successful in preventing barbarian incursions than in the 1st and 2nd centuries. This may have been due to heavier barbarian pressure, and/or to the practice of keeping large armies of the best troops in the interior, depriving the border forces of sufficient support.