Constantine was born on 27 February, c. AD 272 in the city of Naissus, a time where the unity of the Empire was threatened by the breakaway wars of the Palmyrene Empire.[29][30] The city—which is modern day Niš in Serbia—was part of the Dardania province of Moesia.[29] His father was Flavius Constantius[j] an Illyrian who was born in the same region (then called Dacia Ripensis)[34][35][31] and a native of the province of Moesia.[36] His original full name, as well as that of his father, is not known.[37][38] His praenomen is variously given as Lucius, Marcus and Gaius.[38] Whatever the case, praenomina had already disappeared from most public records by this time.[39] He also adopted the name "Valerius", the nomen of emperor Diocletian, following his father's ascension as caesar.[38][37]

Constantine probably spent little time with his father[40] who was an officer in the Roman army, part of Emperor Aurelian's imperial bodyguard. Being described as a tolerant and politically skilled man,[41] Constantius advanced through the ranks, earning the governorship of Dalmatia from Emperor Diocletian, another of Aurelian's companions from Illyricum, in 284 or 285.[36] Constantine's mother was Helena, a Greek woman of low social standing from Helenopolis of Bithynia.[42][43][44][45][46] It is uncertain whether she was legally married to Constantius or merely his concubine.[47] His main language was Latin, and during his public speeches he needed Greek translators.[48]

Head from a statue of the emperor Diocletian

Bust of Maximian, Diocletian's co-emperor

In April 286, Diocletian declared Maximian, another colleague from Illyricum, his co-emperor. Each emperor would have his own court, his own military and administrative faculties, and each would rule with a separate praetorian prefect as chief lieutenant.[49] Maximian ruled in the West, from his capitals at Mediolanum (Milan, Italy) or Augusta Treverorum (Trier, Germany), while Diocletian ruled in the East, from Nicomedia (İzmit, Turkey). The division was merely pragmatic: the empire was called "indivisible" in official panegyric,[50] and both emperors could move freely throughout the empire.[51] In 288, Maximian appointed Constantius to serve as his praetorian prefect in Gaul. Constantius left Helena to marry Maximian's stepdaughter Theodora in 288 or 289.[

Following Galerius' recognition of Constantine as caesar, Constantine's portrait was brought to Rome, as was customary. Maxentius mocked the portrait's subject as the son of a harlot and lamented his own powerlessness.[105] Maxentius, envious of Constantine's authority,[106] seized the title of emperor on 28 October 306. Galerius refused to recognize him but failed to unseat him. Severus was sent against Maxentius in April 307,[107] but during the campaign, Severus' armies, previously under command of Maxentius' father Maximian, defected, and Severus was seized and imprisoned.[108] Maximian, brought out of retirement by his son's rebellion, left for Gaul to confer with Constantine. He offered to marry his daughter Fausta to Constantine and elevate him to augustan rank. In return, Constantine would reaffirm the old family alliance between Maximian and Constantius and offer support to Maxentius' cause in Italy. Constantine accepted and married Fausta in Trier in summer 307.[k] Constantine gave Maxentius his meagre support, offering Maxentius political recognition.[112]

Constantine remained aloof from the Italian conflict, however. Over the spring and summer of 307, he had left Gaul for Britain to avoid any involvement in the Italian turmoil;[113] now, instead of giving Maxentius military aid, he sent his troops against Germanic tribes along the Rhine. In 308, he raided the territory of the Bructeri and made a bridge across the Rhine at Colonia Agrippinensium (Cologne). In 310, he marched to the northern Rhine and fought the Franks. When not campaigning, he toured his lands advertising his benevolence and supporting the economy and the arts. His refusal to participate in the war increased his popularity among his people and strengthened his power base in the West.[114] Maximian returned to Rome in the winter of 307–308 but soon fell out with his son. In early 308, after a failed attempt to usurp Maxentius' title, Maximian returned to Constantine's court.[115]

On 11 November 308, Galerius called a general council at the military city of Carnuntum (Petronell-Carnuntum, Austria) to resolve the instability in the western provinces. In attendance were Diocletian, briefly returned from retirement, Galerius, and Maximian. Maximian was forced to abdicate again and Constantine was again demoted to caesar. Licinius, one of Galerius' old military companions, was appointed augustus in the western regions. The new system did not last long: Constantine refused to accept the demotion and continued to style himself as augustus on his coinage, even as other members of the Tetrarchy referred to him as a caesar on theirs. Maximinus was frustrated that he had been passed over for promotion while the newcomer Licinius had been raised to the office of augustus and demanded that Galerius promote him. Galerius offered to call both Maximinus and Constantine "sons of the augusti",[116] but neither accepted the new title. By the spring of 310, Galerius was referring to both men as augusti.[117]

Maximian's rebellion[edit]

A gold solidus of "Unconquered Constantine" with the god Sol Invictus behind him, struck in AD 313. The use of Sol's image stressed Constantine's status as his father's successor, appealed to the educated citizens of Gaul, and was considered less offensive than the traditional pagan pantheon to the Christians.[118]

In 310, a dispossessed Maximian rebelled against Constantine while Constantine was away campaigning against the Franks. Maximian had been sent south to Arles with a contingent of Constantine's army, in preparation for any attacks by Maxentius in southern Gaul. He announced that Constantine was dead and took up the imperial purple. In spite of a large donative pledge to any who would support him as emperor, most of Constantine's army remained loyal to their emperor, and Maximian was soon compelled to leave. When Constantine heard of the rebellion, he abandoned his campaign against the Franks and marched his army up the Rhine.[119] At Cabillunum (Chalon-sur-Saône), he moved his troops onto waiting boats to row down the slow waters of the Saône to the quicker waters of the Rhone. He disembarked at Lugdunum (Lyon).[120] Maximian fled to Massilia (Marseille), a town better able to withstand a long siege than Arles. It made little difference, however, as loyal citizens opened the rear gates to Constantine. Maximian was captured and reproved for his crimes. Constantine granted some clemency but strongly encouraged his suicide. In July 310, Maximian hanged himself.[119]

In spite of the earlier rupture in their relations, Maxentius was eager to present himself as his father's devoted son after his death.[121] He began minting coins with his father's deified image, proclaiming his desire to avenge Maximian's death.[122] Constantine initially presented the suicide as an unfortunate family tragedy. By 311, however, he was spreading another version. According to this, after Constantine had pardoned him, Maximian planned to murder Constantine in his sleep. Fausta learned of the plot and warned Constantine, who put a eunuch in his own place in bed. Maximian was apprehended when he killed the eunuch and was offered suicide, which he accepted.[123] Along with using propaganda, Constantine instituted a damnatio memoriae on Maximian, destroying all inscriptions referring to him and eliminating any public work bearing his image.[124]

The death of Maximian required a shift in Constantine's public image. He could no longer rely on his connection to the elder Emperor Maximian and needed a new source of legitimacy.[125] In a speech delivered in Gaul on 25 July 310, the anonymous orator reveals a previously unknown dynastic connection to Claudius II, a 3rd-century emperor famed for defeating the Goths and restoring order to the empire. Breaking away from tetrarchic models, the speech emphasizes Constantine's ancestral prerogative to rule, rather than principles of imperial equality. The new ideology expressed in the speech made Galerius and Maximian irrelevant to Constantine's right to rule.[126] Indeed, the orator emphasizes ancestry to the exclusion of all other factors: "No chance agreement of men, nor some unexpected consequence of favour, made you emperor," the orator declares to Constantine.[127]

The oration also moves away from the religious ideology of the Tetrarchy, with its focus on twin dynasties of Jupiter and Hercules. Instead, the orator proclaims that Constantine experienced a divine vision of Apollo and Victory granting him laurel wreaths of health and a long reign. In the likeness of Apollo, Constantine recognised himself as the saving figure to whom would be granted "rule of the whole world",[128] as the poet Virgil had once foretold.[129] The oration's religious shift is paralleled by a similar shift in Constantine's coinage. In his early reign, the coinage of Constantine advertised Mars as his patron. From 310 on, Mars was replaced by Sol Invictus, a god conventionally identified with Apollo.[130] There is little reason to believe that either the dynastic connection or the divine vision are anything other than fiction, but their proclamation strengthened Constantine's claims to legitimacy and increased his popularity among the citizens of Gaul.[131]

Diocletian had chosen Nicomedia in the East as his capital during the Tetrarchy[227]—not far from Byzantium, well situated to defend Thrace, Asia, and Egypt, all of which had required his military attention.[228] Constantine had recognised the shift of the empire from the remote and depopulated[why?] West to the richer cities of the East, and the military strategic importance of protecting the Danube from barbarian excursions and Asia from a hostile Persia in choosing his new capital[229] as well as being able to monitor shipping traffic between the Black Sea and the Mediterranean.[230] Licinius' defeat came to represent the defeat of a rival centre of pagan and Greek-speaking political activity in the East, as opposed to the Christian and Latin-speaking Rome, and it was proposed that a new Eastern capital should represent the integration of the East into the Roman Empire as a whole, as a centre of learning, prosperity, and cultural preservation for the whole of the Eastern Roman Empire.[231] Among the various locations proposed for this alternative capital, Constantine appears to have toyed earlier with Serdica (present-day Sofia), as he was reported saying that "Serdica is my Rome".[232] Sirmium and Thessalonica were also considered.[233] Eventually, however, Constantine decided to work on the Greek city of Byzantium, which offered the advantage of having already been extensively rebuilt on Roman patterns of urbanism during the preceding century by Septimius Severus and Caracalla, who had already acknowledged its strategic importance.[234] The city was thus founded in 324,[235] dedicated on 11 May 330[235] and renamed Constantinopolis ("Constantine's City" or Constantinople in English). Special commemorative coins were issued in 330 to honor the event. The new city was protected by the relics of the True Cross, the Rod of Moses and other holy relics, though a cameo now at the Hermitage Museum also represented Constantine crowned by the tyche of the new city.[236] The figures of old gods were either replaced or assimilated into a framework of Christian symbolism. Constantine built the new Church of the Holy Apostles on the site of a temple to Aphrodite. Generations later there was the story that a divine vision led Constantine to this spot, and an angel no one else could see led him on a circuit of the new walls.[237] The capital would often be compared to the 'old' Rome as Nova Roma Constantinopolitana, the "New Rome of Constantinople".[225][238] 

Beginning in the mid-3rd century, the emperors began to favour members of the equestrian order over senators, who had a monopoly on the most important offices of the state. Senators were stripped of the command of legions and most provincial governorships, as it was felt that they lacked the specialised military upbringing needed in an age of acute defense needs;[265] such posts were given to equestrians by Diocletian and his colleagues, following a practice enforced piecemeal by their predecessors. The emperors, however, still needed the talents and the help of the very rich, who were relied on to maintain social order and cohesion by means of a web of powerful influence and contacts at all levels. Exclusion of the old senatorial aristocracy threatened this arrangement.

In 326, Constantine reversed this pro-equestrian trend, raising many administrative positions to senatorial rank and thus opening these offices to the old aristocracy; at the same time, he elevated the rank of existing equestrian office-holders to senator, degrading the equestrian order in the process (at least as a bureaucratic rank).[266] The title of perfectissimus was granted only to mid- or low-level officials by the end of the 4th century.

By the new Constantinian arrangement, one could become a senator by being elected praetor or by fulfilling a function of senatorial rank.[267] From then on, holding actual power and social status were melded together into a joint imperial hierarchy. Constantine gained the support of the old nobility with this,[268] as the Senate was allowed to elect praetors and quaestors in place of the usual practice of the emperors directly creating magistrates (adlectio). An inscription in honor of city prefect Ceionius Rufus Albinus states that Constantine had restored the Senate "the auctoritas it had lost at Caesar's time".[269]

The Senate as a body remained devoid of any significant power; nevertheless, the senators had been marginalised as potential holders of imperial functions during the 3rd century but could dispute such positions alongside more upstart bureaucrats.[270] Some modern historians see in those administrative reforms an attempt by Constantine at reintegrating the senatorial order into the imperial administrative elite to counter the possibility of alienating pagan senators from a Christianised imperial rule;[271] however, such an interpretation remains conjectural, given the fact that we do not have the precise numbers about pre-Constantine conversions to Christianity in the old senatorial milieu. Some historians suggest that early conversions among the old aristocracy were more numerous than previously supposed.[272]

Constantine considered Constantinople his capital and permanent residence. He lived there for a good portion of his later life. In 328, construction was completed on Constantine's Bridge at Sucidava, (today Celei in Romania)[287] in hopes of reconquering Dacia, a province that had been abandoned under Aurelian. In the late winter of 332, Constantine campaigned with the Sarmatians against the Goths. The weather and lack of food reportedly cost the Goths dearly before they submitted to Rome. In 334, after Sarmatian commoners had overthrown their leaders, Constantine led a campaign against the tribe. He won a victory in the war and extended his control over the region, as remains of camps and fortifications in the region indicate.[288] Constantine resettled some Sarmatian exiles as farmers in Illyrian and Roman districts and conscripted the rest into the army. Constantine reconquered the South of Dacia and the new frontier in Dacia was along the wall and ditch called Brazda lui Novac line supported by new castra.[289] Constantine took the title Dacicus maximus in 336.[290]

In the last years of his life, Constantine made plans for a campaign against Persia. In a letter written to the king of Persia, Shapur, Constantine had asserted his patronage over Persia's Christian subjects and urged Shapur to treat them well.[291] The letter is undatable. In response to border raids, Constantine sent Constantius to guard the eastern frontier in 335. In 336, Prince Narseh invaded Armenia (a Christian kingdom since 301) and installed a Persian client on the throne. Constantine then resolved to campaign against Persia. He treated the war as a Christian crusade, calling for bishops to accompany the army and commissioning a tent in the shape of a church to follow him everywhere. Constantine planned to be baptised in the Jordan River before crossing into Persia. Persian diplomats came to Constantinople over the winter of 336–337, seeking peace, but Constantine turned them away. The campaign was called off, however, when Constantine became sick in the spring of 337