Imperial Roman army in the context of "Legio II Augusta"

In modern scholarship, the "late" period of the Roman army begins with the accession of the Emperor Diocletian in AD 284, and ends in 480 with the death of Julius Nepos, 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 – 284 AD) 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 combat performance.

The Praetorian Guard (Latin: cohortes praetoriae) was the imperial guard of the Imperial Roman army that served various roles for the Roman emperor including being a bodyguard unit, counterintelligence, crowd control and gathering military intelligence.

During the Roman Republic, the Praetorian Guards were escorts for high-ranking political officials (senators and procurators) and were bodyguards for the senior officers of the Roman legions. In 27 BC, after Rome's transition from republic to empire, the first emperor of Rome, Augustus, designated the Praetorians as his personal security escort. For three centuries, the guards of the Roman emperor were also known for their palace intrigues, by whose influence upon imperial politics the Praetorians could overthrow an emperor and then proclaim his successor as the new caesar of Rome. In AD 312, Constantine the Great disbanded the cohortes praetoriae and destroyed their barracks at the Castra Praetoria.

A collegium (pl.: collegia) or college was any association in ancient Rome that acted as a legal entity. Such associations could be civil or religious.The word collegium literally means "society", from collega ("colleague"). They functioned as social clubs or religious collectives whose members worked towards their shared interests. These shared interests encompassed a wide range of the various aspects of urban life; including political interests, cult practices, professions, trade, and civic services. The social connections fostered by collegia contributed to their influence on politics and the economy; acting as lobbying groups and representative groups for traders and merchants.

Some collegia were linked to participating in political violence and social unrest, which resulted in the suppression of social associations by the Roman government. Following the passage of the lex Julia during the reign of Julius Caesar as consul and dictator of the Roman Republic (49–44 BC), and their reaffirmation during the reign of Caesar Augustus as princeps senatus and imperator of the Roman Army (27 BC – 14 AD), collegia required the approval of the Roman Senate or the Emperor in order to be authorized as legal bodies.

The Legio IV Italica ("Italian Fourth Legion") was a legion of the Imperial Roman army raised in AD 231 by emperor Alexander Severus. The legion remained in existence as late as AD 400.

Legio I Italica ("First Italian Legion") was a legion of the Imperial Roman army founded by emperor Nero on September 22, 66 (the date is attested by an inscription). Labeled Phalanx Alexandri Magni and originally destined to the east, it was instead employed in Italy during the year of four emperors. It was later stationed at Novae, near modern-day Svishtov (Bulgaria). There are still records of the I Italica on the Danube border at the beginning of the 5th century. The emblem of the legion was a boar.

Legio XI Claudia ("Claudius' Eleventh Legion") was a legion of the Imperial Roman army. The legion was levied by Julius Caesar for his campaign against the Nervii. XI Claudia dates back to the two legions (the other was the XIIth) recruited by Julius Caesar to invade Gallia in 58 BC, and it existed at least until the early 5th century, guarding lower Danube in Durostorum (modern Silistra, Bulgaria).

The auxilia (Classical Latin: [au̯kˈsɪli.a], lit. 'auxiliaries') were introduced as non-citizen troops attached to the citizen legions by Augustus after his reorganisation of the Imperial Roman army from 27 BC. By the 2nd century, the Auxilia contained the same number of infantry as the legions and, in addition, provided almost all of the Roman army's cavalry (especially light cavalry and archers) and more specialised troops. The auxilia thus represented three-fifths of Rome's regular land forces at that time. Like their legionary counterparts, auxiliary recruits were mostly volunteers, not conscripts.

The Auxilia were mainly recruited from the peregrini, free provincial subjects who did not hold Roman citizenship and constituted the vast majority of the population in the 1st and 2nd centuries (c. 90% in the early 1st century). In contrast to the legions, which only admitted Roman citizens, members of the Auxilia could be recruited from territories outside of Roman control.

The Bar Kokhba refuge caves are natural caves that were used for shelter by Jewish refugees during the later phases of the Bar Kokhba revolt. Most of the refuge caves were located in the Judaean Desert, nestled within steep cliffs far away from settlements, many overlooking the Dead Sea and the Jordan Valley. Some were also found in ravines flowing into the Dead Sea, while others were nestled within the Judaean Mountains. Unlike the other two hideout systems used by the rebels, the man-made rock-cut hiding complexes, and the hard-to-reach cliff shelters which often contain hewn installations, the refuge caves remained largely untouched by human intervention.

Jews taking shelter in refuge caves aimed to escape the Roman army during its suppression of the revolt. These caves are thought to have offered sanctuary to those in the eastern Judaean Mountains and the Jordan Valley. Some caves show signs of successful refuge, while others contain skeletal remains of adults and children, indicating deaths due to starvation, thirst, or encounters with Roman forces, as evidenced by the construction of siege camps and the discovery of arrowheads embedded in cave ceilings.