In historiography, the late or later Roman Empire, traditionally covering the period from 284 CE to 641 CE, refers to the Roman Empire's history during the era of late antiquity. It was a time of significant transformation in Roman governance, society, and religion. Diocletian's reforms, including the establishment of the tetrarchy, aimed to address the vastness of the empire and internal instability. The rise of Christianity, legalized by Constantine the Great in 313 CE, profoundly changed the religious landscape, becoming a central force in Roman life. Simultaneously, barbarian invasions, particularly by the Goths and the Huns, weakened the Western Roman Empire, which collapsed in 476 CE. In contrast, the Eastern Roman Empire endured, evolving into the Byzantine Empire and laying the foundations for medieval Europe.
The era of the Later Roman Empire ended when Muslim armies conquered much of the Byzantine Empire's Near Eastern territories, which were incorporated into the newly emerged Rashidun Caliphate in the 640s and the 650s.
Evidence
Histories
In comparison with previous periods, studies on later Roman history are based on diverse but mainly biased written sources. Completed around 314, Lactantius's work about the Diocletianic Persecution, titled On the Death of the Persecutors, is an early example of prejudiced narrative. Hagiographies—Christian martyrs' and ascetics' biographies—form the period's most distinctive literary genre. The Martyrs of Palestine by Eusebius, Bishop of Caesarea, introduced it in the early 4th century, but a later work, the Life of Anthony about the Egyptian hermit, Anthony the Great set a template for further works. Eusebius' Life of Constantine about the first Christian emperor is a useful collection of letters and official documents. In contrast with classical literature, Hagiographic works regularly presented women as leading characters. Examples include the Life of Macrina about a wealthy and pious aristocrat Macrina the Younger.
With his Church History, Eusebius originated another new literary genre with the focus on Christian missionaries, church leaders, martyrs and heretics. This first church history was revised and resumed by Rufinus in 402. Books written by Socrates of Constantinople, Sozomen and Theodoret are the principal sources of ecclesiastic life until the mid-5th century. Orosius was the first scholar to integrate elements of classical and church history in the 420s. With his History against the Pagans, he wanted to demonstrate that recent calamities cannot be regarded as a punishment for the suppression of traditional Roman religion. Only three church historians' works survived from the 6th century: Zacharias Rhetor, John of Ephesus and Evagrius Scholasticus focus on theological debates. Later church histories, primarily destined to demonstrate the effects of divine providence on human life, seldom provide sufficient information for a deeper analysis of secular history. The is of the utmost importance for the study of the otherwise poorly documented early 7th century. A late source, Theophanes the Confessor's 9th-century Chronographia, is invaluable for the military history of the 620s.
Most information about military and political history has been preserved in secular historians' works. When writing of events familiar to them or their acquaintances, they are mostly reliable. Aurelius Victor and an unknown author completed short imperial biographies in the second half of the 4th century, allegedly using a common source. Around 370 two imperial secretaries, Eutropius and Festus, completed concise accounts of Roman history. Pagan Greek officer Ammianus Marcellinus "has a claim to be the finest Latin historian of any period", according to historian Stephen Mitchell, although only fragments of his Histories survived. Likewise only fragments are known from the works of Ammianus' continuator, Sulpicius Alexander. Scholars studying 5th-century Roman history can primarily rely on a 10th-century collection of fragments from earlier Greek authors' works. One of them, Priscus, wrote a detailed report of his visit at Attila the Hun's court in 449. The pagan Zosimus, the sole prominent later Roman historian whose full work survived, blames Christianity for the quick decline of the Roman Empire. The last outstanding Roman historian, Procopius completed detailed accounts of Emperor Justinian I's rule. His Wars covers military actions. His Buildings provides a list of the achievements of Justinian's building program, but archaeological evidence sometimes contradicts it. He summarizes his true views of Justinian and Justinian's inner circle in the Secret History, describing him as a wicked and unscrupulous figure surrounded by intrigues and scandals. The events of the second half of the 6th century are best known from the fragmentary works of Agathias and Menander the Guardsman. Agathias emphasizes the effect of unexpected events on history, Menander mainly cover diplomacy. The early-7th-century Theophylact Simocatta is the least reliable later Roman historian: both his chronology and topography are chaotic.
Legal texts and inscriptions
The systematic collection of legal texts commenced in the late Roman period. The Code of Theodosius contains about 2,500 entries and covers the period between 335 and 437. The Code of Justinian expands the Code of Theodosius with rulings issued by emperors between 437 and 529. Both legal compilations are important sources of state administration, although their actual application is unproven. The early 5th-century is a useful source of the empire's civil and military administration even if it likely contains exaggerated data: both military commanders and high-ranking civil servants tended to emphasize the importance of their office by giving overestimated numbers to official data collectors. In comparison with the classical age, late Roman inscriptions are available in lesser quantity. Although collective ovations for dignitaries were still regularly commemorated in public places, in this period they were made mainly in honor of imperial officials instead of local leaders as it had been common in the previous centuries.
Archaeology
Archaeological finds also abound, although "they remain understudied" (as Mitchell emphasizes it in 2015). The systematic study of archaeological evidence intensified after the dating system of late Roman pottery stabilized.
Background
Looking back from the early 3rd century, the Roman historian Cassius Dio concluded that the Roman Empire had descended "from a kingdom of gold to one of iron and rust" after Emperor Marcus Aurelius' death in 180 AD. Cassius' words obviously reflect the Roman senators' aversion to the Severan emperors, because other written sources and archaeological evidence indicate that the empire recovered during their reign between 193 and 235. As a surviving element of Roman republican traditions, Roman emperors had been in theory no more than , or first among the senators during the first centuries of the monarchy. This notion of equality was manifest at the relatively high level of informality in the imperial court. Distance between emperors and Roman citizens increased and the ceremony of prostration was first documented during the Severans' reign. In 212, Emperor Caracalla granted full Roman citizenship to his all free subjects except for the , that is aliens who had been forced into submission or admitted to the empire.
The last Severan emperor, Severus Alexander, was assassinated by his own troops in 235. During the following fifty years, twenty emperors ruled the empire in quick succession, and most of them were killed by mutinous soldiers. With the emergence of the militant Sasanian Empire, Rome ceased to be the sole great power in the Near East. In the west, the new tribal confederations of the Franks, Alemanni, Sarmatians and Goths made regular incursions deep into Roman territory. The central government's instability reaffirmed secessionist movements in the periphery. In the west, a rebel provincial governor, Postumus ruled a "Gallic Empire" from 259; in the east, Queen Zenobia established an independent Palmyrene Empire in 267. Both breakaway states were destroyed by Emperor Aurelian in the 270s. As the continuous payment of soldiery could be secured only by the regular debasement of the Roman silver coins, the , inflation became uncontrollable. Inflation increased the significance of taxes in kind, particularly the —the compulsory grain supply to the army—and the —the mandatory military transport.
The mid-3rd century saw a period of cooling and drought, well documented in many regions. During previous years of drought, the exceptional ecological conditions of the fertile Nile valley had helped the Roman authorities to overcome famine in other regions, but the floods of the Nile were abnormally weak from 244 to 248. Furthermore, the deadly pandemic now known as the Plague of Cyprian first hit the Mediterranean in 249. Cyprian, Bishop of Carthage, after whom the plague is named, attributed the calamities to the "old age of the world", but the pagans blamed the Christians' reluctance to worship the ancient gods. The size of the Christian communities had significantly grown in large urban centers like Rome, Antioch, Alexandria and Carthage in the early 3rd century. The Christians were outlawed for their alleged opposition to traditional Roman values, but they were only sporadically persecuted. A drastic change came with Emperor Decius' edict compelling all Romans to make sacrifices to the gods in 249. Non-compliant Christians were executed or forced into exile and the purge continued until Emperor Gallienus put an end to it in 260.
With Gallienus' successor, Claudius Gothicus the military aristocracy of the Roman provinces on the Middle Danube took control of the Roman state. Located at the intersection of overland routes connecting the empire's eastern and western part, these provinces were a principal venue of military operations and recruitment. Typically born into families of long military tradition, the "barracks emperors" were mainly extremely conservatives, but they did not hesitate to overturn traditional principles of state administration for practical considerations.
History
Tetrarchy
The Illyrian Diocletian was a genuine representative of the soldier emperor's reformist zeal. He was proclaimed emperor at a meeting of senior officers at Nicomedia in November 284. He recognized that he could not rule the vast empire alone and made his former comrade-in-arms the Pannonian Maximian his co-ruler, first, in 285, as Caesar (or junior emperor), a year later, as Augustus. The diarchy—the rule of two co-emperors—resulted in the informal division of the empire: Diocletian mostly ruled in the east (including Illyricum and Egypt), and Maximian in the west. In 293, Diocletian instituted a tetrarchy—four co-emperors' joint rule—by appointing two Illyrian officers Constantius Chlorus and Galerius as Caesars. The tetrarchs repelled pillaging raids by the neighboring tribes and launched offensive campaigns against them. New border fortresses were built along the Danube and a selective settlement program was introduced, allowing some Carpians to move from their north-Danubian homeland to Pannonia and Moesia. The Sassanian ruler Narseh invaded Armenia, a buffer state under Roman suzerainty, and routed Galerius in 296. Reinforced by fresh troops from the Danubian provinces, Galerius defeated Narseh in Armenia and sacked the Persian capital Ctesiphon. Peace was restored when Narseh acknowledged the Romans' suzerainty over Armenia and the neighboring Caucasian Iberia, and surrendered some border provinces in 299.