Crisis of the Third Century in the context of "Diocletian"

In modern historiography, the Western Roman Empire were the Roman Empire's western provinces, collectively, during any period in which they were administered separately from the eastern provinces by a separate, independent imperial court. Particularly during the period from AD 395 to 476, there were separate, coequal courts dividing the governance of the empire into the Western provinces and the Eastern provinces with a distinct imperial succession in the separate courts. The terms Western Roman Empire and Eastern Roman Empire were coined in modern times to describe political entities that were de facto independent; contemporary Romans did not consider the Empire to have been split into two empires but viewed it as a single polity governed by two imperial courts for administrative expediency. The Western Empire collapsed in 476, and the Western imperial court in Ravenna disappeared by 554, at the end of Justinian's Gothic War.

Though there were periods with more than one emperor ruling jointly before, the view that it was impossible for a single emperor to govern the entire Empire was institutionalized by emperor Diocletian following the disastrous civil wars and disintegrations of the Crisis of the Third Century. He introduced the system of the Tetrarchy in 286, with two senior emperors titled Augustus, one in the East and one in the West, each with an appointed subordinate and heir titled Caesar. Though the tetrarchic system would collapse in a matter of years, the East–West administrative division would endure in one form or another over the coming centuries. As such, the unofficial Western Roman Empire would exist intermittently in several periods between the 3rd and 5th centuries. Some emperors, such as Constantine I and Theodosius I, governed, if briefly, as the sole Augustus across the Roman Empire. On the death of Theodosius in 395, the empire was divided between his two infant sons, with Honorius as his successor in the West governing briefly from Mediolanum then from Ravenna, and Arcadius as his successor in the East governing from Constantinople.

Augustus (born Gaius Octavius; 23 September 63 BC – 19 August AD 14), also known as Octavian (Latin: Octavianus), was the founder of the Roman Empire, who reigned as the first Roman emperor from 27 BC until his death in AD 14. The reign of Augustus initiated an imperial cult and an era of imperial peace (the Pax Romana or Pax Augusta) in which the Roman world was largely free of armed conflict. The Principate system of government was established during his reign and lasted until the Crisis of the Third Century.

Octavian was born into an equestrian branch of the plebeian gens Octavia. Following the assassination of Julius Caesar in 44 BC, Octavian was named in Caesar's will as his adopted son and heir, and inherited Caesar's name, estate, and the loyalty of his legions. He, Mark Antony, and Marcus Lepidus formed the Second Triumvirate to defeat the assassins of Caesar. Following their victory at the Battle of Philippi (42 BC), the Triumvirate divided the Roman Republic among themselves and ruled as de facto oligarchs. The Triumvirate was eventually torn apart by the competing ambitions of its members; Lepidus was exiled in 36 BC, and Antony was defeated by Octavian's naval commander Marcus Agrippa at the Battle of Actium in 31 BC. Antony and his wife Cleopatra, the Ptolemaic queen of Egypt, killed themselves during Octavian's invasion of Egypt, which then became a Roman province.

This list of Roman civil wars and revolts includes civil wars and organized civil disorder, revolts, and rebellions in ancient Rome (Roman Kingdom, Roman Republic, and Roman Empire) until the fall of the Western Roman Empire (753 BC – AD 476). For the Eastern Roman Empire or Byzantine Empire after the division of the Empire in West and East, see List of Byzantine revolts and civil wars (AD 330–1453). For external conflicts, see List of Roman external wars and battles.

From the establishment of the Roman Republic in 509 BC until the 1st century BC, there were a sparse number of civil wars. But with the Crisis of the Roman Republic (134–44 BC), a period of considerable political instability began. The cause of the late Roman Republican civil wars is contested, as is whether the wars were the cause of, or caused by, the end of the Roman Republic. Regardless, a nearly constant stream of civil wars marked the end of the Roman Republic and heralded the rise of the Roman Empire in 27 BC. The first century of Empire was marked by widespread revolt through territory Rome had captured in the preceding centuries. The second century AD was relatively peaceful, with a limited number of revolts. Political instability returned to the Empire with the Crisis of the Third Century (235–284 AD), which saw at least 26 civil wars in just 50 years as usurpers sought the imperial throne. The fourth and fifth centuries AD were characterized by a regular rising of usurpers. The overthrow of the last Western Roman emperor in AD 476 by the Germanic king Odoacer marked the final civil war or revolt, as well as the end of the Western Roman Empire.

The tetradrachm /ˈtetrəˌdræm/ (Ancient Greek: τετράδραχμον, romanized: tetrádrachmon) was a large silver coin that originated in Ancient Greece. It was nominally equivalent to four drachmae. Over time the tetradrachm effectively became the standard coin of the Antiquity, spreading well beyond the borders of the Greek World. As a result, tetradrachms were minted in vast quantities by various polities in many weight and fineness standards, though the Athens-derived Attic standard of about 17.2 grams was the most common.

Because of their large size, tetradrachms were often used by various states or rulers to advertise themselves or to deliver political messages. Popularity of the tetradrachm outlived the political independence of the Greeks and it remained in wide circulation in the Mediterranean up until Crisis of the Third Century, while debased varieties persisted in India and Central Asia into early Middle Ages.

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.