The Low Roman, along with the High Roman, forms part of the historiographical division of the Roman Empire as seen by French-speaking historians.^{[Notes 1]}

While these terms are widely used, the date of the transition from the High to the Low Roman Empire is the subject of debate. Some historians suggest that the Low Roman began at the end of the Antonine dynasty (192 AD), others with the overthrow of the Severan dynasty (235 AD), and others with the beginning of the reign of Diocletian (284-305).^{[Notes 2]} On the other hand, there is virtually unanimous agreement that the end of the Roman Empire coincides with the end of the Western Roman Empire in 476.^{[Notes 3]}

In place of the period of military anarchy that had seen a rapid succession of emperors chosen by the army, Diocletian wanted to substitute a cooperative system called "tetrarchy", in which two emperors called "Augustus" would choose two assistants called "Caesars", who would replace them on their departure, choosing two new Caesars themselves. This system, which required a great deal of goodwill and altruism, only lasted one generation, and the following one, Constantine I, son of the Caesar and later Augustus Constantius Chlorus, put an end to this co-optation system and returned to the dynastic system, dividing the empire between his sons and nephews on his death. This first Constantinian dynasty lasted just one generation, until one of the three brothers, Constantius, took over the domains of the other two on their death. It was succeeded, after the brief interlude of Emperor Julian, a relative of Constantine I, by the Valentinian dynasty, which lasted only a short time in the East, being replaced by the Theodosian dynasty after the death of its first representative, Valens, in 376. In the West, it continued for five generations, notably during the long reign of Valentinian III (423-455). However, its representatives soon fell under the influence of generals of barbarian origin who, after Valentinian III's death, installed several fanto emperors on the throne, until Odoacer proclaimed the destitution of Romulus Augustulus and returned the imperial ornaments to Constantinople in 476.

This Low Roman period differed from the preceding one in several ways: the administration underwent numerous changes, notably under Diocletian and Constantine I; the economy saw the creation under Constantine of a gold coin, the "solidus", which would remain the basis of Byzantium's monetary system for centuries; the great cities lost their importance to the large estates that competed with them; finally, Christianity, initially persecuted, spread until it became the state religion with the Edict of Thessalonica in 380.

The term "Low Roman" dates back to 1752, when the first of 28 volumes of Charles Le Beau's^[1] Histoire du Bas Roman was published between 1752 and 1817. The use of the adjective "bas" was not negative: it simply referred to the period closest to us, as opposed to "haut". Nevertheless, the term Low Roman long had a pejorative connotation among Lumières historians, who saw it as a period of decadence marked by monarchical absolutism and the power of the Church, succeeding the Republic and the Empire.^[1] Today, while the trend is to rehabilitate this period, some historians prefer more neutral names such as Late Roman Empire^[2] or Late Antiquity, following the German (Spätrömische Zeit, Spätantike) or Italian (tardo Impero, tardoantico) terminologies. Whatever the case, the long-established term Low Roman is still frequently used, although authors still debate when it began.

Some suggest the end of the Antonine dynasty (192 AD), others the overthrow of the Severan dynasty (235 AD), still others the beginning of the reign of Diocletian (284-305):

• From 193, the end of the Antonine dynasty represents the beginning of the empire's crisis; some even suggest 180, to classify Emperor Commodus in this period.^[3]
• From 235, the overthrow of the Severan dynasty ushered in an unstable period of some fifty years, known as military anarchy.
• Finally, at the end of this period of unrest, the year 284, is chosen by other authors, such as Paul Petit.^[4] The beginning of Diocletian 's reign saw the principate replaced by a collegiate regime, whose absolutism was inspired by Eastern monarchies.

Although more numerous than for the preceding period, the written sources we have for the Low Roman often reflect conflicts between pagan and Christian authors, as well as within the Christian Church itself, between the so-called "Nicene"^{[Notes 4]} and Arian authors.^{[Notes 5]}

The first author of these "chronographies" to become so popular in Byzantium was Eusebius (c. 265 - 339), bishop of Caesarea, who escaped the persecutions of Diocletian and was a close associate of Emperor Constantine I. His "Chronicle" (in two books up to 325) was the starting point of the genre, as was his "Ecclesiastical History" (ten books up to 324). His "Vita Constantinii magni", recounting the life and work of Constantine I, is a relevant collection of letters and documents.^[5]

Summarized by Rufinus of Aquileia (c. 345 - c. 411) in 402, this History of the Church was continued by Socrates the Scholastic or of Constantinople (c. 380 - 450) for the years 306 - 439, by Sozomen (400 - c. 450) for the years 324 - 415 and Theodoret of Cyr (c. 393 - c. 458) for the years 325 - 428. The latter was continued by Evrage le Scholastique (c. 536 - after 594), whose work on the years 431 - 593 is also important for secular history.^[6]

Added to this Christian literature are the writings of the Church Fathers of this period: Athanasius of Alexandria (c. 296/298 - 373), Gregory of Nazianzus (329 - 390), Basil of Caesarea (329 - 379), Gregory of Nyssa (335 - c. 395), John Chrysostom (between 344-349 - 407) and many others. Also important for their historical content are the acts of the first ecumenical councils, the first four of which were held before the fall of Rome (Nicaea I in 325, Constantinople I in 381, Ephesus in 431 and Chalcedon in 451).^[6]

Among the pagan authors was Zosimus (late 5th century - early 2nd century), who blamed Christianity for the decline of the Roman Empire.^[7] Emperor Julian (sometimes called "Julian the Philosopher" or "Julian the Apostate", r. 361-363) himself helped to promote traditional Greek philosophy, along with his contemporaries Themistios (317 - 388) and Libianius (314 - 392 or 393).^[8] But the most important historian of this period was undoubtedly Ammianus Marcellinus (c. 330 - c. 395). Although clearly a pagan, he tried to be objective, and his main work, Res gestae in 31 books, covers the period from 96 to 378; however, only the part corresponding to the years 353 to 378 has been preserved. His work was continued by Sulpicius Alexander (late fifth century - early fifth century), author of a "History" of which only fragments survive, and which extends up to the death of the Roman emperor Valentinian II in 392.^[9][10]

Finally, a document from the 5th century, the Notitia Dignitatum (Register of Dignitaries), is a Roman administrative document that has been revised several times, providing a list of the hierarchical organization of civil and military functions in both the western and eastern parts of the Roman Empire. It provides a good overview of the state of the Roman army and administration in the Low Roman after the reforms of Diocletian and Constantine I, even if various updates have introduced inconsistencies, especially with regard to the army of the Western Empire.^[11]

Theodosius Codex (Codex Theodosius) contains some 2,500 entries containing constitutions or laws issued since the reign of Constantine I, between 335 and 437. It was followed by the Code of Justinian (Codex Justinianus) for the years from 437 to 529. Both are useful sources for state administration. Political, economic, social and religious issues are covered, giving a good idea of the condition of the inhabitants, even if many of these constitutions remained dead letters or were only half-implemented.^[12][13]

Born into a modest Dalmatia family, Diocletian rose through the military ranks to become commander of Emperor Carus' cavalry (r. 282-283). After the deaths of Carus (r. 282 - 283) and his son Numerian (r. 283 - 284) during the Persian campaign, he was proclaimed emperor by his troops in Nicomedia.^[14][15] His task was to put an end to the period of military anarchy which, from 235 to his accession, had seen a succession of "soldier-emperors".

To this end, he took a series of radical measures:

• He separated civil and military power as far as possible, and divided the powers of the various office-holders.
• He reduced the power of the Senate of Rome, moving it to places where the military situation demanded it: Trier, Milan, Aquileia, Nicomedia, Antioch.
• He strengthened imperial power: the Principate instituted by Augustus was replaced by the Dominate, making the emperor a sacred person.
• He split up the provinces, creating a new intermediate structure, the dioceses, which would link the provinces with the prefectures of the Praetorium responsible for governing the empire, one controlling the West and Africa, the other the East and Egypt.^[16]

But Diocletian not only had to fight enemies from within, like Carinus, he also had to secure the empire's borders, which were under attack from all sides. Unable to face all the threats alone while he was detained in Pannonia, in December 285 he enlisted the help of another soldier, Maximian, to whom he entrusted, with the title of Caesar, the task of putting an end to the ravages of the barbarians on the Rhine frontier and those of the Bagaudes in Gaul. The following year, when Carausius declared himself emperor in Brittany (England), he elevated Maximian to the rank of Augustus, simply marking his own primacy by placing himself under the protection of the god "Jovius", whereas Maximian would be under that of a simple hero, Hercules.^[17][18] At a meeting in Milan, the two men agreed that the task was too big for two people. To help them, they adopted two valuable generals from Illyricum: Maximian adopted Constantius Chlorus in March 293 and Diocletian Galerius in May.^[18][19]

The tetrarchy was thus born: at the top, two Augustinians assisted by two Caesars who were to replace the Augustinians when they decided to retire. Gradually, each of them took charge of a part of the empire: Diocletian took charge of the East, with Nicomedia and Antioch as his headquarters; Maximian took charge of Africa, Italy and Spain, with Milan as his headquarters; Constantius Chlorus took charge of Gaul and Brittany (England), with Trier as his headquarters; finally, Galerius took charge of Illyricum, whose borders varied, with Sirmium (today Sremska Mitrovica in Serbia) as his headquarters.^[18]

For a time, this system put an end to the incessant changes of emperors in the interior, and ensured the security of the borders. It functioned smoothly until May 1, 305, when both Augustans abdicated on the same day, handing over the reins of power to their respective Caesars, Galerius in the case of Diocletian, Constantius in that of Maximian.^[20] In Nicomedia, Diocletian presented his soldiers with Galerius' nephew, Maximin Daia, who became the new Caesar, while in Milan, Severus was similarly appointed.^[21]

It only took a year for discord to set in among the new tetrarchs with the death of Constantius in July 306. Galerius promoted Severus to the rank of Augustus. Meanwhile, Constantius' son Constantine was acclaimed emperor in Brittany (England) by troops loyal to his father.^[22] At the same time, Maximian's son Maxentius, furious at being left out of the arrangements, defeated Severus, forced him to abdicate and had him assassinated in 307. The principle of cooptation advocated by Diocletian was replaced by that of dynastic inheritance. The situation became so complex that by 310, there were seven emperors all claiming to be Augusti, a number reduced to four by 311: Maximin Daia (in Asia Minor, Syria and Egypt), Licinius (in Illyricum and the Balkans), Constantine (in Gaul, Spain and Brittany) and Maxentius (in Italy and Africa).^[23][24] It took Constantine eleven years (313 - 324) to restore the unity of the empire at the expense of Lucinius, who had become the sole ruler of the East.

The end of the tetrarchy marked a rainfall to the principle of heredity. Although he had his eldest son Crispus, born of a first marriage, murdered, Constantine appointed his three sons from a second marriage as Caesars: Constantine II in 317, Constantius II in 324 and Constans in 333.^[25][26] In December 335, he entrusted each with responsibility for a part of the empire: Constantine II was put in charge of Gaul, Spain and Brittany; Constantius II received Asia, Syria and Egypt; Constantine I, Illyricum, Italy and Africa. He also elevated a half-nephew, Delmace, son of Constantine's half-brother Flavius Dalmatius,^{[Notes 6]} to the dignity of Caesar and entrusted him with Thrace, Macedonia and Achaia, while he gave another nephew, Hannibalianus, the title of King of Kings and the yet-to-be-conquered crown of Armenia.^[27][28]

Equally important, Constantine's era marked the beginning of the end of paganism as the state religion, the political as well as the religious basis of the system conceived by Diocletian (see "Religion" below). The Edict of Milan of 313 established freedom of religion not only for Christians, but also for those professing other faiths.^[29] At the beginning of the 4th century, Christians represented between 10 and 15% of the empire's population, but heresies were already tearing the new Church apart: Donatism in Africa, Arianism throughout the empire, and particularly in the East.^[30]

In 330, Constantine chose the ancient city of Byzantium to found a new capital to which his name would remain attached, Constantinople, even though it was then known as "Second Rome". The city's strategic importance lay in its ability to intervene rapidly against barbarian invasions, both on the Danube and in Mesopotamia; its commercial importance lay in its position as the point of arrival of one of the trade routes from the Far East and another from Northern Europe, as well as being an important stopover on the pilgrimage route to Jerusalem; and finally, its location in an East that was booming economically and culturally, while Italy was in decline.^[31][32]

Constantine completed the administrative, financial and monetary reforms begun under Diocletian.

He strengthened the separation between civil and military power. Provincial governors were to be responsible only for civil administration, leaving border protection to career generals.^[33] To prevent these same governors from becoming so ambitious as to think of usurping the purple, he retained the Diocletian multiplication of provinces, while ensuring that they were self-sufficient: he abolished certain provinces that were too small, but reunited Numidia and divided Moesia.^[33]

Alongside the Prefect of the Praetorium,^{[Notes 7]} a sort of prime minister in charge of the bureaucracy that formed part of his private council or comitatus, Constantine appointed four regional prefects in 326: one for Gaul, based in Trier; one for Africa, based in Carthage; one for Italy, probably based in Milan; and one for Illyricum, based in Sirmium (and later in Thessalonica).^[34][35] And while the prefect would remain responsible for army recruitment, supplies and equipment,^[33] he would lose the leadership of the troops, which would be entrusted to two career soldiers, the magister peditum and magister equitum (lit: chief of infantry; chief of cavalry), while a magister officiorum (lit: head of departments) would be in charge of the palatine bureaucracy and the civil service as a whole.^[36]

For civil administration, a magister officiorum (lit: master of offices) supervised not only the emperor's personal guard (scholae), but also the four main ministries or offices (scrinaia). In addition, he created a private council or comitatus (lit: group of companions) composed mainly but not exclusively of senators.^[37]

With Rome retaining its Senate, Constantine created a new one for his "New Rome". He would invite Roman senators who were ready to move, and add new high-ranking officials. Since Augustus, the dignity of senator (ordo senatorius) had been hereditary, but it was necessary to hold a magistracy in order to be admitted to the Senate.^[38] From the time of Constantine I onwards, entry to the Senate was by virtue of a prefecture. The Senate also included senior state officials such as the Master of Offices and the Master of Soldiers (General-in-Chief), as well as provincial governors and retired officials. The number of senators was multiplied from the original 600 to 2,000 under Constantius II.^[39]

But the great novelty of this administration was the increase in the number of civil servants and the reorganization of the civil service, which became a kind of civilian militia, reproducing the structure of the army. The aim was to bind civil servants more closely to the emperor, who became a kind of "general-in-chief" of the civil service.^[33] A host of notaries, agents (agentes in rebus), nearly 1,000 civil servants in the 5th century,^[40] and various other employees turned the Roman Empire into a veritable bureaucracy.^[41]

All these reforms led to a considerable increase in public spending, which Diocletian had already increased. Constantine's search for new resources led him to introduce new taxes.^[42] Faced with the looming financial crisis, immediately after his victory over Maxentius, he replaced theaureus, which had depreciated sharply, with a new gold coin, the solidus (or solidus aureus), which was to form the basis of a monetary system that would remain exceptionally stable in the Eastern Empire until the 11th century.^[43]

Before his death, Constantine I had divided his empire between his three sons and two nephews. Although events and chronology are confused,^[44] it seems that the army refused to accept Constantine's nephews as part of the division. As the three sons wanted to keep the whole empire for themselves, the result was a vast massacre within the imperial family, in which both nephews and Constantine's half-brothers perished. On September 9, at Viminacium in Moesia, the three surviving brothers divided up the dioceses: Constantine II, the eldest, took the West, i.e. Gaul, Brittany and Hispania; Constantius II retained the East, adding the diocese of Thrace; Constantine, who was still only fourteen, seems to have been placed under Constantine II's guardianship, with theoretical jurisdiction over Italy, Africa and Panonia.^[44]

Despite his youth, Constantine was an ambitious young man who soon sought to free himself from his brother's tutelage. As early as 339, he rebelled against his brother,^[45] who marched against him across Italy with his troops.^[46] He was killed in an ambush near Aquileia.^[46] Constant then took control of his brother's territories, and there were now only two emperors: Constantius II in the East and Constant in the West.

Brutal towards Donatist Christians, hateful towards pagans to whom he forbade traditional sacrifices, an adversary of the Arians, Constant was also malicious towards the aristocracy of Rome, while increasing the burden of taxation and bureaucracy on the population. Given his unpopularity in all circles, it's hardly surprising that he fell victim to a military conspiracy led by his former general in the Rhine armies, Magnentius, in early 350. Attempting to flee to Hispania, he was caught at Castrum Helenae (Elne, near Perpignan) and put to death. As he left no heir, Constantius remained sole emperor, but had to face the usurper Magnentius.^[47][48]

Acclaimed emperor on January 18, 350 at Augustodunum (Autun), Magnentius, former head of Constant I's personal guard, was immediately recognized by Gaul, Brittany (England), Africa and Cyrenaica. Held back in the East by the war against the Persians, Constantius II was unable to avenge his brother immediately. It was not until the following year that a truce with the Persians allowed him to set out to meet Magnentius. The two men met in the Balkans at Sirmium. The war pitted two largely barbarian armies against each other: Magnentius' army of Germans defending the Rhine frontier, and Constantius II's army of Illyrians, hostile to the Germans. It was a war of attrition that was only resolved in September 351 at Mursa (Osijek on the Drava). Losses were enormous on both sides; the Eastern emperor had the upper hand, but Magnentius managed to escape to Gaul, where he was finally defeated near Gap (Hautes-Alpes in France).^[49][50][51]

Magnentius' usurpation was to have far-reaching consequences in both East and West. In the East, Constantius II, now aged around twenty-five, was asserting his personality: in the religious sphere, he took an increasingly violent stand for Arianism; in the political sphere, he became distrustful and easily cruel towards both his generals and the Caesars he had appointed. In the West, he had not hesitated to launch King Chnodomar's Alamanni against Magnentius. Invaded by them, Gaul was to experience some difficult years.^[49][50]

Constantius continued to rule alone for almost a decade. Busy with the war against the Persians and realizing the need for an assistant, he successively appointed two survivors of the massacre of Constantine I's half-brothers, Constantius Gallus from 351 to 354, whom he had executed, and then Constantine's half-brother Julian, whom he invested with strictly military powers. The antithesis of the career military man, Julian nevertheless covered himself in glory at the battle of Strasbourg in 357. Three years later, his troops, having learned that Constantius wanted to send them to Persia, rebelled and proclaimed their commander emperor. Constantius had to abandon Persia to fight his cousin: he was to die en route, but not before having had the wisdom to make Julian his heir, thus preserving the unity of the empire.^[52][53]

Julian's short reign marked both the continuation of the Constantinian dynasty and the failure of the rainfall to paganism.

A nephew of Constantine I, he was the last survivor, along with his half-brother Gallus, of the younger branch of the descendants of Emperor Constantius Chlorus. Nothing foreshadowed the destiny that was to be his. Raised as a Christian under the guidance of the Arian bishops Eusebius of Nicomedia and George of Cappadocia, he was six years old when most of the family of Constantine I 's second marriage were massacred. Julian and Gallus escaped with their lives, but were excluded from public life. Isolated in the fortress of Macellum in Cappadocia, Julian devoured the Christian and pagan books in his tutor's rich philosophical library.^[54][55] In 347, he was allowed to return to Constantinople, but preferred to continue his studies in Nicomedia, Pergamon and Athens.

In November 355, Constantius made him Caesar against his will and sent him to Gaul, where his unexpected military and administrative qualities were revealed.^[56] In spite of himself, he was acclaimed by his soldiers. His twenty months or so in power were characterized by great reforming activity, the rainfall of paganism and an ill-fated campaign against the Persians.^[57]

Going against the centralizing policy of Constantius, he favored the autonomy of the cities, reformed the excesses of the bureaucracy, particularly the tax collectors, and simplified and accelerated the justice system. A philosopher prince, he reduced court ceremonial and abolished many sinecures, as well as most of the posts of notary andagentes in rebus, officials who acted as controllers and spies for the central government.^[58]

In the very first months of his reign, he issued an edict of tolerance, reversing the persecutory measures of Constant and Constantius: he returned to pagans their property and temples, while giving them permission to celebrate sacrifices; he extended this tolerance to all Christian sects; he protected Jews whose traditionalist and ethnic religion he felt had been distorted by Christianity; and he had the Temple of Jerusalem rebuilt at state expense. Soon, however, this tolerance turned to hostility towards Christians, who were forbidden to teach philosophy.^[59][60][61]

In Antioch, at the end of 362/beginning of 363, he prepared a preventive campaign against the Persians, hoping to repeat Trajan 's campaign of 116. At the head of a 65,000-strong army, he penetrated Persia. An initial victory on the banks of the Tigris opened the road to Ctesiphon. But the Persians' scorched-earth policy made his advance difficult. When he arrived at Ctesiphon and realized he could not take the city, he ordered a retreat. On June 26, during a rearguard action, he was hit by a horseman's spear and died.^[62] This campaign marked the end of the great expeditions, far from the empire's traditional frontiers.^[63][64][61]

Hastily elected by the generals of a routed army, Jovian (r. June 363 - Feb. 364) had no choice but to accept the terms of a peace dictated by Shapur II, before undertaking a hasty retreat during which he himself was to die, probably asphyxiated in his tent by the fumes of a brazier.^[65]

His successor was the result of a compromise between senior military and civil dignitaries: their choice fell on one of their own, Valentinian (r. 364-375), then tribune of the scholae secundae scutariorum, a Pannonian like his predecessor, a moderate Christian renowned for his energy and honesty.^[66] This choice was the result of a compromise between the Gallic and Eastern clans; he was therefore required to appoint a co-emperor, which Valentinian did by choosing his brother, Valens (r. 364 - 378), to whom he entrusted the East.^[67][68]

The dynasty he founded was to have a limited duration in the East, being replaced by the Theodosian dynasty after the death of its first representative, Valens, in 378 at the famous Battle of Adrianople.^[69] In the West, it continued until the end of the reign of Valentinian III (r. 424-455).

Having established his headquarters in Gaul and residing mainly in Trier from 365 to 375,^[70] Valentinian made border defense his priority. Near Amiens, he fell gravely ill in 366 and, to avoid succession problems, had to appoint his young son Gratian co-emperor.^[71] He survived, however, and after further campaigns on the Rhine, in Britain and Africa, died of apoplexy after a heated encounter with Quadian ambassadors at Brigetio in 376.^[72] Gratian assumed the succession, but his generals doubted the military abilities of this studious sixteen-year-old, and proclaimed the young Flavius Valentinianus (Valentinian II, r. 375-392), four years his junior and Valentinian's son by his second wife Justina, co-emperor. Valentinian adopted the young man and entrusted him with the theoretical rule of Illyricum, Africa and Italy.^[73]

Gratian ruled the western part of the empire from 367 to 383, and Valens the eastern part until 378. Established in Trier, Gratian had to contend with the Alamanni who crossed the Rhine in 378,^[74] as well as the Goths who ravaged Thrace the same year and Illyricum the following year.^[75] But it was his internal and religious policies that brought about his downfall. His dismissal of pagan civil servants in favor of Christian ones, combined with his lack of interest in military affairs and his predilection within the army for his personal guard of Aryan deserters, alienated large sectors of the ruling class.^[76] In the summer of 383, on his way to Raetia, where the Alamanni were in turmoil, Magnus Maximus, the "come" of Britannia, was acclaimed emperor by his troops. He crossed the English Channel and confronted Gratien near Paris. Abandoned by his troops, he had to flee to the Alps. He was assassinated in Lyon during a meeting with his adversary.^[77][78]

In the East, after putting down the revolt of Procopius, a relative of Emperor Julian, in 366,^[79] Valens embarked on a campaign against the Goths. Based at Marcianopolis in Thrace (today Devnya in Bulgaria), he succeeded two years later in driving the Goths back to Transylvania. Transferring his capital to Antioch, he launched a campaign against the Persians to recover the provinces abandoned by Jovian.^[80] It took him seven years to succeed, but he was unable to complete his victory: driven out of their territories by the Huns, the Visigoths had settled in 376 near the Black Sea in Silistria (Bulgaria). Some of them were allowed to settle in the empire,^[81][82] but exploited by unscrupulous Roman military leaders, they rebelled and Valens had to send two armies against them. On August 9, 378, his own army was defeated and the emperor killed at the battle of Andrinople.^[83] As Valens left no male heir, it fell to Gratian, now senior Augustus, to appoint a successor. Realizing that he could not cope alone with the peril threatening both East and West, Gratian turned to a Spanish general, Theodosius, to whom he entrusted the East as well as the dioceses of Dacia and Macedonia, which until then had been part of his own domain. Theodosius was promoted to Augustus at Sirmium on January 19, 379.^[82][84][85]

Theodosius I (r. 379-395) was to be the first emperor to rule almost constantly from Constantinople.^[86][87] As early as 383, he proclaimed his six-year-old eldest son, Arcadius, co-emperor. He did the same with his other son, Honorius, in 393.^[88] During his reign, he faced three major challenges. The first was the battle against two usurpers: Magnus Maximus (usurper 384-388) who, after defeating Gratian, had seized the entire prefecture of Gaul and occupied Rome and the whole of Italy to the detriment of Valentinian II,^[89] and Eugenius, proclaimed co-emperor of the Western Romans in 392 following the death of Valentinian II by the Frankish general Arbogast, whom Theodosius^[90] refused to recognize, opposing him to his own son, Honorius. The second was the rapid spread of Christianity. The Edict of Thessalonica in May 380 made Christianity the official state religion. But there was resistance from pagans and Jews alike, as well as from heretics among the Christians themselves who did not share the Nicene Creed (325), including the Manichaeans.^[91] Finally, the barbarians continued to exert pressure on the edges of the empire. After the defeat at Andrinople, Theodosius no longer had an army to oppose them. While waging guerrilla war on those who continued to ravage the Balkans, he chose to integrate and assimilate those who wished to join his new army. In October 382, he signed a treaty with the Goths, recognizing them for the first time and settling them along the Danube as a "Foederati".^[92]

Theodosius was to be the last emperor to rule a unified empire. On his death, eighteen-year-old Arcadius became senior emperor in the East and ten-year-old Honorius junior emperor in the West.^[93] For contemporaries, however, this was not a division of the empire, but rather a new division of tasks. The dynastic ties between the two branches of the family were only broken with the accession of Leo I, of Thracian origin, in 457; laws and decrees were signed by both emperors and, in theory, were applicable in both parts of the empire.^[94] This was also the period when, either because of their youth or weakness of character, emperors became the playthings of their immediate advisors: army generals like Stilicho in the west, prefects of the Praetorium like Rufinus in the east. It was also a period when, in the West, several usurpers rose to prominence, such as Constantine III (407-411), Maximus (409-411) and Priscus Attale (409 - 410 and 414 - 415) under the reign of Honorius, as well as Joannes (423-425), who was overthrown by Theodosius II in favor of Valentinian III (r. 425-455).

It was also a period in which the consequences of Theodosius' policy of integrating barbarians into the army and assimilating their peoples into the empire became apparent. Many barbarians found themselves in command of the army, facing former compatriots, while their populations, though partly assimilated, had little sense of loyalty to the empire. Alaric, king of the Visigoths since 395, invaded Italy three times, culminating in the sack of Rome in 410, after persuading the Senate to appoint Priscus Attale emperor.^[95][96]

In 407, General Constantinus (Constantine III) abandoned Britain, where his soldiers had proclaimed him emperor, to settle in Trier and then Arles; however, he was unable to prevent the Vandals, Alans and Suevi from crossing the Pyrenees and settling in Hispania.^[97] Finally, this was the period when Honorius, realizing that he could no longer keep control of England, once the army had left, had to send letters to these cities encouraging them to defend themselves alone.^[98][99]

As Valentinian III had no male heir, the Theodosian dynasty, which was to end with the death of Marcian in the East in 457, died out with him in the West in 455.^[100] On his death, the senator Petronius Maximus (r. March 455- May or June 455) seized the throne, forcing Valentinian's widow, Licinia Eudoxia, to marry him in order to establish dynastic legitimacy, but this succession was not recognized by the Eastern emperor, Marcian, who was too old to govern both empires. This marked the beginning of an irremediable decline for the Western Empire, which fell victim internally to the seizure of power by various illegitimate individuals, and externally to invasions from Africa (the Vandals) and Central Europe (the Visigoths).

Following the assassination of Petronius Maximus in 455 and the sacking of Rome by the Vandal king Genseric, the Gallo-Roman aristocracy had the Arverne Avitus (r. July 455 - October 456) proclaimed emperor in Arles with the support of the Visigoth king Theodoric II, who needed his help to fight the Vandals.^[101] Acknowledged by the Emperor of the East, Leo I, he was not recognized by the people of Rome, who had not participated in his choice. He was overthrown by Patrice Ricimer, with the support of the Roman aristocracy. Several months of hesitation followed, before Majorian proclaimed himself Augustus on December 28, 457.^[102] But his authority no longer extended much beyond Italy, southern Gaul and southern Spain; the Visigoths were already masters of much of Gaul and Spain. On his rainfall from a failed expedition to reconquer Spain, he was arrested and executed by Ricimer.^[103]

With Majorian out of the way, Ricimer became the true ruler of the Western Empire. But being of barbarian origin,^{[Notes 8]} he could not accede to the throne himself. So he appointed a succession of puppet emperors in quick succession: Libius Severus, known as Severus III (r. 461-465),^[104] Anthemius (r. 467-472),^[105] Olybrius (r. April - November (?) 472).^[106] Once again, Leo I refused to recognize Ricimer's choice, and he died in August 472. His nephew, a young Burgundian prince by the name of Gondebaud, then had the head of his personal guard, Flavius Glycerius or Glycerius, appointed emperor (r. March 473). Leo I having died in the meantime, the new emperor, Zeno (r. February 474 - January 475; August 476 - April 491), appointed Julius Nepos, governor of Dalmatia, to restore order in the West.^[107] Nepos landed at Ravenna in early 474 and put to flight Glycerius, who, without an army, sought to reach Rome, where the Senate closed the city gates to him. Taken prisoner, Glycerius was deposed and appointed bishop of Salone in Dalmatia.^[108]

On June 24, 474, Julius Nepos (r. June 474-August 475) was acclaimed emperor by his small band, but without the support of the Romans, who regarded him as a Byzantine. Senators conspired with the army's general-in-chief, Orestes, from a Roman family in Pannonia, to overthrow Nepos. Content to act as regent, Orestes had his son Romulus Augustulus, a teenager of around 15, appointed emperor on October 31, 475.^[109] But the state coffers were empty, and the military had long been without pay. Led by an officer of the imperial guard, Odoacre, son of the king of the Skires and as such with great influence over the other barbarian contingents, they demanded from Orestes a third of the lands of Italy. When he refused, they revolted and proclaimed Odoacre king of Italy on August 23, 476. Orestes fled first to Pavia, then to Piacenza, where he was caught and beheaded, while his son Romulus Augustulus escaped with his life after abdicating to the Senate. All that remained for Odoacre to do was to return the imperial ornaments to Emperor Zeno, signifying that he was now the sole emperor of East and West.^[109]

In itself, this event did not represent a profound break with the past. In Italy, which had become a Germanic kingdom, it had become customary for the new emperor to be chosen after a few months by the country's true master. This time, however, it was a definitive break and, writing in 551, the historian Jordanès made no mistake when he wrote: "Thus, did the Western Empire and the principate of the Roman people, which the first of the Augustans, Octavian Augustus, had held from the year 709 of the founding of the City, perish with this Augustulus in the year 622 of the reign of the emperors who had preceded him".^[110]

While the date of the end of the Western Empire coincides with the deposition of Romulus Augustus, it remains unclear for the Eastern Empire, where the transition to the Byzantine Empire is not marked by such a radical event, and varies according to authors from the foundation of Constantinople in 330 to the accession of Heraclius in 610.^[111]

In theory, nothing changed between the High and Low Roman periods. There were still one or two emperors, a Senate (now two), magistrates, provincial governments and municipalities.^[112] However, their roles and powers evolved as the emperor's divine character became institutionalized.^[113]

By Augustus and the Principate, the princeps had become a true monarch, while republican institutions, though maintained, lost their powers.^{[Notes 9]} And while the emperor was no longer a god (imperial worship was abolished under Constantius), he had become the one chosen by God.^[114] The acclamation of a new emperor by the army, and his ratification by the Senate and the people, merely confirms this divine choice.^[115] Hence the "sacred" character of everything connected with his person, and the ceremonial organized within a court where titles and functions multiplied, the most oriental aspect of which was the rite of "adoration" demanded by Diocletian.^[116][114] Another feature, as mentioned above, was the rainfall of the dynastic idea, which had been undermined during the third-century crisis and military anarchy. With the exception of Jovian and Valentinian, all the emperors tried (some clumsily) to link themselves to Constantine's family: Valentinian's son Gratian married the posthumous daughter of Constantius, while Theodosius married the last daughter of Valentinian and Justina, Galla.^[117]

Reporting to the prince was a Privy Council, initially made up of members of the equestrian order, whom Constantine later transformed into senators and who, after 337, took the name of Sacred Consistory (Sacrum Consistorium). The four permanent members of this Consistory were the "count of sacred largesse" (minister of finance) and the "count of private property" (minister of private patrimony), the master of offices (in charge of bureaucracy) and the quaestor of the sacred palace (questor sacri palatii), who was the emperor's spokesman at the Consistory.^[118]

One of the radical changes of the Low Roman was the growth of the bureaucratic apparatus, the result of the concentration of power in the hands of the prince. Whereas the central administration employed fewer than 1,000 civil servants under the first emperors, by the end of the 4th century there were more than 35,000.^[119]

As for the Senate of Constantinople, created by Constantine to counterbalance that of Rome, the number of its members rose to 2,000 as Constantius II and his immediate successors brought in friends, courtiers and various provincial officials. Although its powers were reduced, it continued to enjoy a high reputation and influence, bringing together incumbent or retired holders of the highest state offices, such as the Master of the Militia and the Prefects of the Praetorium, important officials such as proconsuls, vicars and military governors of the provinces (duces), as well as provincial governors and other high-ranking officials.^[120][121]

By the 260s, the empire numbered some 50 provinces. By the early 4th century, after Diocletian's reforms, there were almost 100.^{[Notes 10]} Diocletian grouped them into twelve new districts called "dioceses". Each diocese was headed by a "vicar" (vicarius) who reported to one of the two prefects of the Praetorium. Originally the principal military advisors to the two Augustinians, these prefects gradually became their prime ministers, enjoying extensive authority in almost every sphere of government, be it military, judicial, financial or administrative.^[122] As Constantine's sons divided up his empire, each had his own prefect in charge of a specific geographical area, so that the Praetorian prefecture went from being a personal function to designating an administrative division grouping together a number of dioceses. From the end of the 4th century onwards, there were four prefectures of the Praetorium (Gaul, Italy, Illyricum and the East), a number that remained stable until Justinian.^{[Notes 11][123]}

But while the High Roman, which was essentially made up of cities, municipalities and colonies, could be considered the "golden age" of municipalities, the centralization of power in the Low Roman led to a loss of their autonomy, with the appearance under Diocletian of "city trustees" (logistai) whose powers, (defensor civitatis), who went from being protectors of the poor against the rich, to becoming magistrates in charge of tax collection.^[124][125] Only two cities escaped this system: Rome and Constantinople, both of which had a "Prefect of the City" enjoying great prestige and extensive powers.

In the face of the barbarian invasions that represented the greatest challenge of the Low Roman, the army was an essential component of the state, which various emperors did not hesitate to lead in person, even if it meant losing their lives,^[126] as was the case with Emperors Julian and Valens. It was also within this framework that new emperors such as Jovian and Valentinian ^I continued to be sought, before returning to the dynastic principle.

According to John the Lydian, a 6th-century Byzantine official and writer, Diocletian's army numbered 389,704 men and his navy 45,562. Modern estimates suggest a force of between 400,000 and 600,000 in the mid-4th century.^{[127][128][129]} The vast majority of soldiers were conscripts or the sons of soldiers. Prisoners were also incorporated, including soldiers from defeated armies. Gradually, the number of barbarians increased substantially. The fact that several emperors had to issue edicts punishing those who mutilated themselves to avoid recruitment seems to show that the profession was not popular with all strata of society.^[130]

The army of the Low Roman had a very different face from that of the High Roman, which was essentially a frontier army arranged along a zone called "limes", made up of fortified camps and smaller forts linked by an imposing road network, all designed to ensure security within the empire.^[131] Since Th. Momsenn, experts have debated the respective roles of Diocletian and Constantine in the reorganization of the army).^[132] For Marcel Le Glay, Diocletian made four major changes:

• He increased the number of legions from 39 to 60, often by fragmenting the former legions, some of which saw their strength reduced from 6,000 to 1,000 men. Provinces along the limes generally had two legions and two cavalry detachments (vexillationes).^[133]
• The military structure remained virtually unchanged: the legions, known as "limitanei", were flanked by auxiliary units, cavalry wings (600 men) and infantry cohorts (300 men). However, cavalry wings were increased from 4 to 9, and infantry cohorts from 28 to 37.^[133]
• He rehabilitated or reinforced frontier fortifications: in the East, the "strata Diocletiana" was built, with its network of roads linking forts and encampments; in Egypt, the temple of Amon at Louqsor was transformed into a vast camp housing the "legio III Diocletiana"; on the Rhine limes, fortresses were built which, while smaller than those of the High-Empire, were more numerous.^[134]
• Finally, he organized a special army around the emperor, the comitatus, an imperial guard made up of cavalry and infantry detachments that could intervene as a reserve force and was under the emperor's direct command.^[135]

Constantine completed these reforms by establishing a maneuver army, concentrated within the territory and at the immediate disposal of the command. Under the name of "comitatenses", these field troops made up the bulk of the army. From then on, there were three categories of military personnel:

• On the frontiers, the "ripenses" (litt. "riparians"), soldier-cultivators who took up arms to defend their land and property.
• Inland, units of 1,000 men, the "comitatenses", who enjoyed greater tax benefits than the "ripenses".
• A rapid intervention force made up of "alares" (wings) of cavalry and "cohortales".^[136]

Extrapolations allow us to estimate the population of the Eastern Empire at around 24 million around 350, rising to 30 million under Justinian I after the reconquest of Italy and Africa; the population of the Western Empire is estimated at just under 20 million, an imbalance that would be increased by the development of Constantinople and the Eastern metropolises.^[137] In the 4th and 5th centuries, Constantinople and Alexandria were estimated to have some 500,000 inhabitants, Antioch 200,000 and Thessalonica 140,000.^[138][139]

The crisis of the third century had not only disrupted the political life of the empire; it had also resulted in a serious economic crisis. The n^[140] eed to combat invasions on the one hand, and infighting between generals on the other, led to an increase in military spending, which accounted for half of all state expenditure.^[141] The failure to reform the monetary system under Aurelian (r. 270-275) led to a structural problem for the state and an unprecedented rise in inflation. Barter reappeared as the monetary economy declined.^[142]

The division of provinces, the growth of bureaucracy and Diocletian's reforms of the army only exacerbated this problem.^[143] The emperor attempted to remedy the situation by instituting a tax system based on land (jugum), peasant (caput) and livestock (caput animalium), which required a gigantic census of goods and people in the empire, to be adjusted every five years thereafter, and, finally, a reform of the monetary system.^[144][145] Alongside silver and gold coins, he increased the number of copper coins used for daily transactions, devaluing Aurelian's "nummi" from 5 to 2 denarii. As a result of this devaluation, not only did prices continue to rise, but gold and silver coins were traded at a premium to their face value.^[146][147] As inflation accelerated, he was forced, at the end of 301, to promulgate the "Law of the Maximum", which set maximum prices for foodstuffs and objects of commercial value, and taxed them accordingly.^[148][149]

It fell to Constantine I to make a new reform, returning to a gold basis: the "solidus", which replaced the "aureus", until then the empire's official currency.^[150] The solidus remained the backbone of the Byzantine monetary system for ten centuries,^[151] and was long used as a currency of exchange around the Mediterranean. He also modified the census of state assets, the basis of taxation, which was henceforth to be carried out every fifteen years and henceforth to be known as "indiction".^{[152][Notes 12]} He also introduced new taxes, particularly on the upper classes (the "clarissimes") and towns.

While the state had little involvement in the production, transport or sale of consumer goods under the High Empire, the reforms of Diocletian and Constantine led to a new "interventionism" of the state in economic life, even if this tended more to adapt to market laws than to direct them, with such interventions occurring mainly in times of crisis.^[153] From a social point of view, however, the result was economic monopolization by the "powerful" ("potentes") and social compartmentalization.^[154]

Early Imperial society was divided into "orders" (ordo), where senators and knights enjoyed privileges that were practically self-evident, but where a slave could hope to become a freedman, and a freedman's son not only a citizen in his own right, but even a magistrate.^[155] Ulpian, the great jurist of the Severans in the 3rd century, distinguished for the first time between "little people" (humiliores) and "powerful people" (potentiores; possessores; honestiones)^[156] in Roman society, where all citizens were considered equal before the law. A century later, the favors enjoyed by honestiones were specified by law: for the same offence, honestiones were punished by exile or a fine, while humiliores were punished by death.^[157]

Appealing his decisions to the emperor required further expense and was unlikely to be successful, especially if the emperor was busy fighting a war against the Persians or barbarians.^[158]

While the aim of every senator remained to be appointed consul and to be able to give his name to the year, the consulship was no more than a title, and even the privilege of giving one's name to the year was replaced by the "Indiction".^[159]

Whether they lived in the city and only came to inspect their estates on occasion, or retired to "villae" in the middle of their lands, these "possessores" were increasingly interested in developing their lands and increasing both their income and the patronage they could exert over both their peasants and the municipalities when their lands were located on or near the territory of a city.^[160]

The development of large rural estates began at the very beginning of the Empire, and reached its peak in the 3rd and 4th centuries.^[161] They were owned by wealthy individuals, generally from the increasingly numerous senatorial class, whose members usually lived in the city, where they were associated with large shipping owners and merchants.^[162] On the one hand, they were responsible to the state for the payment of taxes by the estate's tenants; on the other, the state guaranteed them the necessary manpower by increasingly tying smallholders to their land.^[163] From the 4th century onwards, the weakening of municipal governments was to benefit these "possessores", and the large estates tended to become autonomous tax units under the sole responsibility of the provincial governor.^[164]

The situation varied from one region of the empire to another, although large imperial estates were widespread everywhere: first and foremost in Egypt, but also in Italy, Spain and Africa.^[165] In the East, where large landowners often owned land scattered over a vast territory, there were also lands belonging to a temple whose settlers were the "serfs of the god".^[166][167] The same was true of 5th-century Italy, where large estates were made up of scattered domains of varying sizes.^[168]

The High Roman Empire was made up of a group of cities (Latin civitates, Ancient Greek πόλεις / póleis), autonomous communities consisting of a town and the rural territories that depended on it. There were over 900 entities legally recognized as "cities", although only a handful had a population of over 10,000, most were around 1,000 and a few no more than a few hundred.^[169] They served as tax collection centers, headquarters for civil and ecclesiastical authorities, fortifications against enemies and public markets.^[170] While there were cities where a single town played a key role (e.g. Athens as an intellectual center, Alexandria for its port and industry), the vast majority were essentially small-scale, deriving their wealth from the agricultural land around them.^[171]

This municipal council was normally made up of some one hundred members, originally elected and later co-opted by "respectable men", i.e. those with the status of citizens of the city and of well-to-do fortune;^[172] they had to be at least twenty-five years old and have served one term of office as mayor or "duumvir".^[173]

In the Low Roman, the aristocrats who made up the curia were joined by wealthy merchants, businessmen and landowners. Indeed, they were expected to provide funds for the construction and upkeep of public monuments, temples, festivals and games.^[174] They also became responsible for collecting imperial taxes,^[175] feeding and housing troops stationed in their municipe, and running the imperial post (cursus publicus), the costs of which were borne by the landowners whose estates they crossed.^[176]

Although Constantine I had established the curia as an official body, giving its members specific rights and obligations, he and his successors confiscated for the imperial treasury the endowments,^{[Notes 13]} local taxes, land rents and official buildings that had previously belonged to the municipalities.^[177] This burden became financially ruinous for all but the wealthiest, especially in the western part of the empire where the settlement of numerous barbarian groups was disrupting the administration of the empire. As a result, many potential candidates for these positions enlisted in the army or the civil service, or joined the orders, to escape what had once been a highly sought-after honor. To combat this evasion, Constantine not only made the office a compulsory one, but also forbade its members to change their status once appointed.^[178]

In the course of the 5th century, curiales were increasingly recruited from among "notables", i.e. people who were not "ex officio" members of these councils: senators, magnates, former military commanders with large estates, bishops, former high-ranking civil servants who had made their fortune, and so on.^[179][180] Already, however, municipal councils were gradually losing their autonomy, as they became increasingly subject to imperial control, with state agents being dispatched to them. Thus, for example, the "city defenders" (defensores civitatis), instituted by the emperors Valentinian and Valens to protect the weak against the powerful and whose role had been strengthened under Justinian, became the true leaders of the city, presiding over the assembly of curiales, directing finances and exercising municipal justice.^[181] The curia were to disappear definitively during the reign of Leo VI (r. 886-912).^[178]

Although no longer the same as in the period of Cicero or even the High Empire, paganism- a generic term covering a vast array of different religions - remained very much alive in the 4th century. In the upper classes of society, some felt a sense of attachment to the traditional values of Rome in the face of growing barbarization, while others, influenced by Eastern religions and philosophies, became increasingly mystical, moving towards a monotheism that gave one god superiority over all others. This is how Aurelian (r. 270-275) institutionalized the cult of the solar god (Sol Invictus), a divinity that was very popular with the armies of the Danube and to which both the Baal-worshipping Orientals of Emesa and the neo-Platonist elites could adhere. In the lower classes, it was increasingly tinged with magical and astrological practices.^[182][183]

Diocletian's tetrarchy was placed under the protection of the gods of the Roman state; he himself was patronized by the god Jupiter, and Maximian by the hero Hercules. And while the tetrarchs readily accepted the Oriental god Mithras, they - Galerius in particular - vigorously opposed both Christianity and Manichaeism, whose values were irreconcilable with imperial theology, in which the emperor was a member of the family of gods.^[184]

After breaking with Maximian and becoming Caesar, Constantine claimed the protection of Apollo, Sol Invictus, like Claudius Gothicus (r. 268-270), from whom he began to claim descent. His slow conversion began in 312 with his famous battle against Maximian. From 313 to 321, he sought to reconcile his personal beliefs with those of the followers of the religion that had secured his victory, using ambiguous terms such as "summus deus, summa divinita". First came the "Edict of Milan", dated 313; then the Donatist heresy forced him to clarify his position vis-à-vis the Church at the Council of Arles in 314. From 316 to 320, contradictory forces were exerted on him, and his policy was one of balance between Christians and pagans, while legislation began to integrate the Church into the State, giving it the power to have its own courts in 318. The last solar symbols disappeared between 320 and 322.^[185]

It seems that it was only after 324 and his victory over Licinius that he turned definitively to the Christian side, when the title of "Victor" replaced that of "Invictus", signifying the definitive abandonment of solar worship. In 325, he presided over the first Council of Nicaea, where he sought above all to ensure the unity of the empire, proclaiming himself "the bishop of those outside, that is, of all Christians who were not clerics, whether or not they belonged to the empire. In the last years of his life, his religious policy was dominated by two key ideas: reconciliation with the Arians (he was baptized by an Arian bishop) and the weakening of paganism.^[186]

Following Constantine's death, Constantine I (r. 337-350) took control of the West after killing his brother Constantine II (r. 337-340). Like his father and his other brother Constantius II (r. 337-361) in the East, he was determined to spread Christianity and put an end to pagan sacrifices and the practice of magic.^[187] A supporter of orthodoxy and the Nicene creed, he opposed both the Donatists in Africa and the Arians defen^[188] ded by his brother, Constantius II (r. 337-361), who remained faithful to the ideas of his father, Constantine I.^[189]

The short interval of Emperor Julian (r. 361-363), although it showed that paganism was still very much alive in certain sectors of society, was only a flash in the pan,^[190] and saw the triumphant rainfall of orthodoxy under Valentinian (r. 364-375) and Valens (r. 364-378). In the West, which had become largely "Nicene", Valentinian practiced a policy of tolerance, refraining from attacking those who wished to remain pagans and avoiding meddling in Church affairs. Only the Manichaeans in Italy and the Donatists in Africa were repressed, but more because of the social disorder they caused than because of their religious convictions. Valens, operating in an Eastern context where religious struggles were raging, was a convinced Arian who sought to impose his ideas on his Nicene, Homoeusian^{[Notes 14]} and Anomaean opponents by violent means.^{[Notes 15][191]}

After them, Theodosius, for the Eastern Roman Empire, and Gratian, for the Western Roman Empire, made Nicene Christianity the official religion of the State, with the edict of February 28, 380, known as the Edict of Thessalonica: "All peoples must rally to the faith handed down to the Romans by the Apostle Peter, the faith recognized by the Pontiff Damasus and Peter, Bishop of Alexandria, that is, the Holy Trinity of Father, Son and Holy Spirit". Christian doctrine, as defined at the First Council of Nicaea, thus asserted itself not only against the pagans who still existed, but also against the various schismatic Christian Churches, such as the Arians, whose doctrine was once again condemned at the First Council of Constantinople (381). The reign of Theodosius consolidated the alliance between throne and altar, despite conflicts between the emperor and Saint Ambrose, bishop of Milan.

The territorial organization of the Church then developed, modelled on that of the empire: almost every city had its own bishop, and the bishop of the capital of a diocese, the "metropolitan", took authority over the others. In 381, the Council of Constantinople affirmed that the Patriarch of Constantinople would take precedence over the others and become the equal of the Patriarch of Rome, except "in honor". The Church then tended to form a state within the state, enjoying tax privileges and acquiring considerable wealth. On the theological front, the fight against heresy gave Church Fathers such as Basil of Caesarea, Gregory of Nyssa, Gregory of Nazianzus and John Chrysostom the opportunity to deepen their doctrine, which was defined at the many councils of the period.^[192]

While in the 3rd century the Church was still a minority affair, a century later it had become a "mass religion". As a reaction against these compromises with the "world", various Christians, especially in the East, sought to attain the knowledge of God by withdrawing from the world to live a life of mortification and asceticism.^[193][194] This was the starting point for monasticism, which was later to play a considerable political role in the Eastern Empire.

From Gibbon' s "History of the Decline and Fall of the Roman Empire" to Marxist historians, terms such as "decline", "disappearance" and "decadence" have been used to describe the Low Roman Empire.^[195] On the other hand, the work of modern historians^{[Notes 16]} has shown that, while the 3rd century in particular was a period of crisis (rapid succession of emperors, barbarian invasions, fiscal pressure and inflation, social breakdown), the opposite could also be true when worthy emperors such as Gallien, Claudius II or Aurelian reigned long enough to restore order and unity. Similarly, it was never the whole empire that was in crisis. Some provinces were privileged and their cities flourished, while others struggled for survival. Thus, while in the second half of the 3rd century the provinces of Asia Minor were ruined by Persian invasions and Gothic raids, Pamphylia remained a haven of peace, and cities such as Pergé and Sidé flourished. The 4th and 5th centuries, with the great reforms of Diocletian that continued under Constantine and the founding of Constantinople, heralded a new world.

Although it did not outlive its creator, the tetrarchy was a new political concept, as was the dyarchy beginning with the sons of Theodosius. The Christianization of the empire also brought new cultural and religious values.^[196] A new economic and social order was also born. It was these new values that Justinian I (r. 527 - 565) embodied in his efforts to restore the unity and grandeur of the Roman world.

• Late antiquity
• Crisis of the Third Century
• Barracks emperor
• Western Roman Empire

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