Military units similar to or like Imperial Roman army

The armed forces deployed by the Romans throughout the duration of Ancient Rome, from the Roman Kingdom (to c. 500 BC) to the Roman Republic (500–31 BC) and the Roman Empire (31 BC–395 AD), and its medieval continuation, the Eastern Roman Empire. Thus a term that may span approximately 2,205 years , during which the Roman armed forces underwent numerous permutations in composition, organisation, equipment and tactics, while conserving a core of lasting traditions. Wikipedia

The (Latin:, lit. "auxiliaries") were introduced as non-citizen troops attached to the citizen legions by Augustus after his reorganisation of the Imperial Roman army from 30 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. Wikipedia

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. Wikipedia

The history of the Roman Empire covers the history of ancient Rome from the fall of the Roman Republic in 27 BC until the abdication of Romulus Augustulus in AD 476 in the West, and the Fall of Constantinople in the East in AD 1453. Then ruled by Roman emperors beginning with Augustus ((r. Wikipedia

The structural history of the Roman military concerns the major transformations in the organization and constitution of ancient Rome's armed forces, "the most effective and long-lived military institution known to history." From its origins around 800 BC to its final dissolution in AD 476 with the demise of the Western Roman Empire, Rome's military organization underwent substantial structural change. Wikipedia

Roman civilization from the founding of the Italian city of Rome in the 8th century BC to the collapse of the Western Roman Empire in the 5th century AD, encompassing the Roman Kingdom , Roman Republic (509 BC–27 BC) and Roman Empire (27 BC–476 AD) until the fall of the western empire. Italic settlement in the Italian Peninsula, traditionally dated to 753 BC, that grew into the city of Rome and which subsequently gave its name to the empire over which it ruled and to the widespread civilisation the empire developed. Wikipedia