Constantine I

Constantine was born on 27 February 272. While his official birthday is recorded in sources, his year of birth is not, and scholars have given several estimates between 271 and 280, with most leaning for 272 or 273. However, the evidence points to 272 being the correct year. He was born inside the city of Naissus, during a time when the unity of the Empire was threatened by the breakaway wars of the Palmyrene Empire. The city (modern Niš, Serbia) was located in Dardania within the province of Moesia Superior. His father was Flavius Constantius, an Illyrian or, according to his nephew, Julian The Apostate, a Thracian. His original full name, as well as that of his father, is not known. His praenomen is variously given as Lucius, Marcus and Gaius. Whatever the case, praenomina had already disappeared from most public records by this time. He also adopted the name "Valerius", the nomen of emperor Diocletian, following his father's ascension as caesar.

Constantine probably spent little time with his father Constantius, who was an officer in the Roman army, part of Emperor Aurelian's imperial bodyguard. Being described as a tolerant and politically skilled man, Constantius advanced through the ranks, earning the governorship of Dalmatia from Emperor Diocletian, another of Aurelian's companions from Illyricum, in 284 or 285. Constantine's mother was Helena, a Greek woman of low social standing, possibly from Drepanum (later renamed Helenopolis) of Bithynia, which would likely have made her a Greek-speaker. It is uncertain whether she was legally married to Constantius or merely his concubine. Constantine's own language was Latin, and during his public speeches in the church councils, which were held in Greek, he needed Greek translators.

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. 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, and both emperors could move freely throughout the empire. 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.

Diocletian divided the empire again in 293, appointing two caesars to rule over further subdivisions of East and West. Each would be subordinate to his respective augustus but would act with supreme authority in his assigned lands. This system would later be called the Tetrarchy. Diocletian's first appointee for the office of Caesar was Constantius; his second was Galerius, a native of Felix Romuliana. According to Lactantius, Galerius was a brutal, animalistic man. Although he shared the paganism of Rome's aristocracy, he seemed to them an alien figure, a semi-barbarian. On 1 March, Constantius was promoted to the office of Caesar, and dispatched to Gaul to fight the rebels Carausius and Allectus. In spite of meritocratic overtones, the Tetrarchy retained vestiges of hereditary privilege, and Constantine became the prime candidate for future appointment as Caesar as soon as his father took the position. Constantine went to the court of Diocletian, where he lived as his father's heir presumptive.

Constantine received a formal education at Diocletian's court, where he learned Latin literature, Greek, and philosophy. The cultural environment in Nicomedia was open, fluid, and socially mobile; in it, Constantine could mix with intellectuals both pagan and Christian. He may have attended the lectures of Lactantius, a Christian scholar of Latin in the city. Because Diocletian did not completely trust Constantius—none of the Tetrarchs fully trusted their colleagues—Constantine was held as something of a hostage, a tool to ensure Constantius' best behaviour. Constantine was nonetheless a prominent member of the court: he fought for Diocletian and Galerius in Asia and served in a variety of tribunates; he campaigned against barbarians on the Danube in 296 and fought the Persians under Diocletian in Syria in 297, as well as under Galerius in Mesopotamia in 298–299. By late 305, according to some, he had become a tribune of the first order, a tribunus ordinis primi.

Constantine had returned to Nicomedia from the eastern front by the spring of 303, in time to witness the beginnings of Diocletian's "Great Persecution", the most severe persecution of Christians in Roman history. In late 302, Diocletian and Galerius sent a messenger to the oracle of Apollo at Didyma with an inquiry about Christians. Constantine could recall his presence at the palace when the messenger returned and Diocletian accepted the imperial court's demands for universal persecution. On 23 February 303, Diocletian ordered the destruction of Nicomedia's new church, condemned its scriptures to the flames, and had its treasures seized. In the months that followed, churches and scriptures were destroyed, Christians were deprived of official ranks, and priests were imprisoned. It is unlikely that Constantine played any role in the persecution. In his later writings, he attempted to present himself as an opponent of Diocletian's "sanguinary edicts" against the "Worshippers of God", but nothing indicates that he opposed it effectively at the time. Although no contemporary Christian challenged Constantine for his inaction during the persecutions, it remained a political liability throughout his life.

On 1 May 305 Diocletian, as a result of a debilitating sickness taken in the winter of 304–305, announced his resignation. In a parallel ceremony in Milan, Maximian did the same. Lactantius states that Galerius manipulated the weakened Diocletian into resigning and forced him to accept Galerius' allies in the imperial succession. According to Lactantius, the crowd listening to Diocletian's resignation speech believed, until the last moment, that Diocletian would choose Constantine and Maxentius (Maximian's son) as his successors. It was not to be: Constantius and Galerius were promoted to augusti, while Severus and Maximinus, Galerius' nephew, were appointed their caesars respectively. Constantine and Maxentius were ignored.

Some of the ancient sources detail plots that Galerius made on Constantine's life in the months following Diocletian's abdication. They assert that Galerius assigned Constantine to lead an advance unit in a cavalry charge through a swamp on the middle Danube, made him enter into single combat with a lion, and attempted to kill him in hunts and wars. Constantine always emerged victorious: the lion emerged from the contest in a poorer condition than Constantine; Constantine returned to Nicomedia from the Danube with a Sarmatian captive to drop at Galerius' feet. It is uncertain how much these tales can be trusted.

Constantine recognised the implicit danger in remaining at Galerius' court, where he was held as a virtual hostage. His career depended on being rescued by his father in the West. Constantius was quick to intervene. In the late spring or early summer of 305, Constantius requested leave for his son to help him campaign in Britain. After a long evening of drinking, Galerius granted the request. Constantine's later propaganda describes how he fled the court in the night, before Galerius could change his mind. He rode from post-house to post-house at high speed, hamstringing every horse in his wake. By the time Galerius awoke the following morning, Constantine had fled too far to be caught. Constantine joined his father in Gaul, at Bononia (Boulogne) before the summer of 305.

From Bononia they crossed the English Channel to Britain and made their way to Eboracum (modern York), capital of the province of Britannia Secunda and home to a large military base. Constantine was able to spend a year in northern Britain at his father's side, campaigning against the Picts beyond Hadrian's Wall in the summer and autumn. Constantius' campaign, like that of Septimius Severus before it, probably advanced far into the north without achieving great success. Constantius had become severely sick over the course of his reign and died on 25 July 306 in Eboracum. Before dying, he declared his support for raising Constantine as emperor. The Alamannic king Chrocus, a barbarian taken into service under Constantius, then proclaimed Constantine as augustus. The troops loyal to Constantius' memory followed him in acclamation. Gaul and Britain quickly accepted his rule; Hispania, which had been in his father's domain for less than a year, rejected it.

Constantine sent Galerius an official notice of Constantius' death and his own acclamation. Along with the notice, he included a portrait of himself in the robes of an Augustus. The portrait was wreathed in bay. He requested recognition as heir to his father's throne and passed off responsibility for his unlawful ascension on his army, claiming they had "forced it upon him". Galerius was put into a fury by the message; he almost set the portrait and messenger on fire. His advisers calmed him and argued that outright denial of Constantine's claims would mean certain war. Galerius was compelled to compromise: he granted Constantine the title "caesar" rather than "augustus" (the latter office went to Severus instead). Wishing to make it clear that he alone gave Constantine legitimacy, Galerius personally sent Constantine the emperor's traditional purple robes. Constantine accepted the decision, knowing that it would remove doubts as to his legitimacy.

Constantine's share of the empire consisted of Britain, Gaul, and Spain. He commanded one of the largest Roman armies, stationed along the strategically important Rhine frontier. He remained in Britain after his promotion to emperor, driving back the tribes of the Picts and securing his control in the northwestern dioceses. He completed the military bases begun under his father's rule and ordered the region's roads repaired. He then left for Augusta Treverorum (Trier) in Gaul, the Tetrarchic capital of the northwestern Roman Empire. The Franks learned of Constantine's acclamation and invaded Gaul across the lower Rhine over the winter of 306–307. He drove them back beyond the Rhine and captured kings Ascaric and Merogais; the kings and their soldiers were fed to the beasts of Trier Amphitheater in the adventus (arrival) celebrations which followed.

Constantine began a major expansion of Trier. He strengthened the circuit wall around the city with military towers and fortified gates, and he began building a palace complex in the northeastern part of the city. To the south of his palace, he ordered the construction of a large formal audience hall and a massive imperial bathhouse. He sponsored many building projects throughout Gaul during his tenure as emperor of the West, especially in Augustodunum (Autun) and Arelate (Arles). According to Lactantius, Constantine followed a tolerant policy towards Christianity, although he may not have yet adopted the Christian faith. There is no consensus among scholars on Constantine's religious convictions at the beginning of his reign, and some suggest an adoption of Christianity from his youth. Regardless, he probably judged toleration a more sensible policy than open persecution and a way to distinguish himself from the "great persecutor" Galerius. He decreed a formal end to persecution and returned to Christians all that they had lost under the first of the persecuting edicts.

Constantine was largely untried and had a hint of illegitimacy about him; he relied on his father's reputation in his early propaganda, which gave as much coverage to his father's deeds as to his. His military skill and building projects, however, soon gave the panegyrist the opportunity to comment favourably on the similarities between father and son, and Eusebius remarked that Constantine was a "renewal, as it were, in his own person, of his father's life and reign". Constantinian coinage, sculpture, and oratory also show a tendency for disdain towards the "barbarians" beyond the frontiers. He minted a coin issue after his victory over the Alemanni which depicts weeping and begging Alemannic tribesmen, "the Alemanni conquered" beneath the phrase "Romans' rejoicing". There was little sympathy for these enemies; as his panegyrist declared, "It is a stupid clemency that spares the conquered foe."

Following Galerius's 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. Maxentius, envious of Constantine's authority, seized the title of emperor on 28 October 306. Galerius refused to recognise him but failed to unseat him. Severus was sent against Maxentius in April 307, but during the campaign, Severus' armies, previously under command of Maxentius' father Maximian, defected, and Severus was seized and imprisoned. 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. Constantine gave Maxentius his meagre support, offering Maxentius political recognition.

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; 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. 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.

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", but neither accepted the new title. By the spring of 310, Galerius was referring to both men as augusti.

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. 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). 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.

In spite of the earlier rupture in their relations, Maxentius was eager to present himself as his father's devoted son after his death. He began minting coins with his father's deified image, proclaiming his desire to avenge Maximian's death. 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. 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.

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. 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 emphasises 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. Indeed, the orator emphasises 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.

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", as the poet Virgil had once foretold. 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. 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.

By the middle of 310 Galerius had become too ill to involve himself in imperial politics. His final act survives: a letter to provincials posted in Nicomedia on 30 April 311, proclaiming an end to the persecutions, and the resumption of religious toleration.

Eusebius maintains "divine providence [...] took action against the perpetrator of these crimes" and gives a graphic account of Galerius' demise:

"Without warning suppurative inflammation broke out round the middle of his genitals, then a deep-seated fistula ulcer; these ate their way incurably into his innermost bowels. From them came a teeming indescribable mass of worms, and a sickening smell was given off, for the whole of his hulking body, thanks to over eating, had been transformed even before his illness into a huge lump of flabby fat, which then decomposed and presented those who came near it with a revolting and horrifying sight."

Galerius died soon after the edict's proclamation, destroying what little remained of the Tetrarchy. Maximinus mobilised against Licinius and seized Asia Minor. A hasty peace was signed on a boat in the middle of the Bosphorus. While Constantine toured Britain and Gaul, Maxentius prepared for war. He fortified northern Italy and strengthened his support in the Christian community by allowing it to elect Eusebius as bishop of Rome.

Maxentius' rule was nevertheless insecure. His early support dissolved in the wake of heightened tax rates and depressed trade; riots broke out in Rome and Carthage; and Domitius Alexander was able to briefly usurp his authority in Africa. By 312, he was a man barely tolerated, not one actively supported, even among Christian Italians. In the summer of 311, Maxentius mobilised against Constantine while Licinius was occupied with affairs in the East. He declared war on Constantine, vowing to avenge his father's "murder". To prevent Maxentius from forming an alliance against him with Licinius, Constantine forged his own alliance with Licinius over the winter of 311–312 and offered him his sister Constantia in marriage. Maximinus considered Constantine's arrangement with Licinius an affront to his authority. In response, he sent ambassadors to Rome, offering political recognition to Maxentius in exchange for a military support, which Maxentius accepted.

Constantine reunited the empire under one emperor, and he won major victories over the Franks and Alamanni in 306–308, the Franks again in 313–314, the Goths in 332, and the Sarmatians in 334. By 336, he had reoccupied most of the long-lost province of Dacia which Aurelian had been forced to abandon in 271. At the time of his death, he was planning a great expedition to end raids on the eastern provinces from the Persian Empire.

In the cultural sphere, Constantine revived the clean-shaven face fashion of earlier emperors, originally introduced among the Romans by Scipio Africanus (236–183 BC) and changed into the wearing of the beard by Hadrian (r. 117–138). With some departures, such as Julian the Apostate (r. 360–363), this new Roman imperial fashion lasted until the reign of Phocas (r. 602–610) in the 7th century.

The Holy Roman Empire reckoned Constantine among the venerable figures of its tradition. In the later Byzantine state, it became a great honour for an emperor to be hailed as a "new Constantine"; ten emperors carried the name, including the last emperor of the Eastern Roman Empire. Charlemagne used monumental Constantinian forms in his court to suggest that he was Constantine's successor and equal. Charlemagne, Henry VIII, Philip II of Spain, Godfrey of Bouillon, the House of Capet, the House of Habsburg, the House of Stuart, the Macedonian dynasty and the Phokas family claimed descent from Constantine. Geoffrey of Monmouth embroidered a tale that the legendary king of Britain, King Arthur, was also a descendant of Constantine. Constantine acquired a mythic role as a hero and warrior against heathens. In later Byzantine legend, Constantine's building activity was also projected beyond Constantinople. The medieval Patria of Constantinople says that, after subduing the Scythians, he founded Persthlaba, Distra, Pliskouba and Konstantia. His reception as a saint seems to have spread within the Byzantine empire during wars against the Sasanian Persians and the Muslims in the late 6th and 7th century. The motif of the Romanesque equestrian, the mounted figure in the posture of a triumphant Roman emperor, became a visual metaphor in statuary in praise of local benefactors. The name "Constantine" enjoyed renewed popularity in western France in the 11th and 12th centuries. During the Fascist period in Italy in the 20th century, parallels between Constantine and Mussolini became especially popular after the signing of the Lateran Pacts by the Italian State and the Catholic Church in 1929. Mussolini's perceived role in bringing about the historic agreement was sometimes even explicitly compared to Constantine's Edict of Milan. For example, the archbishop of Milan, Cardinal Ildefonso Schuster, claimed that, after sixteen centuries, a second March on Rome had occurred and a second 'religious pact' had been established, linking Mussolini to the spiriti magni of both Constantine and Augustus.

The Niš Constantine the Great Airport is named in honour of him. A large cross was planned to be built on a hill overlooking Niš, but the project was cancelled. In 2012, a memorial was erected in Niš in his honour. The Commemoration of the Edict of Milan was held in Niš in 2013.

Constantine is sometimes associated with the religiopolitical ideology known as Caesaropapism, which epitomises the unity of church and state. However, his association with this ideology has been debated.

Constantine is commemorated annually as a saint primarily by Eastern Christian Churches.

The autocephalous Eastern Orthodox Churches and the Eastern Catholic Churches of the Catholic Church venerate Saint Constantine (Άγιος Κωνσταντίνος) as isapostolos (ισαπόστολος Κωνσταντίνος)—an equal of the Apostles. He and his mother, Saint Helena, are commemorated on 21 May, with liturgical propers composed for the Horologion (e.g., Great Vespers) and Divine Liturgy. Several Orthodox monasteries, shrines and churches claim to have first-class relics of Constantine.

The Coptic Orthodox Church commemorates Saint Constantine on 28 Parmouti.

Tha Maronite Catholic Church commemorates him along with Saint Helena on 21 May.

The Armenian Apostolic Church commemorates Saint Constantine and Saint Helena on the Tuesday of the fourth week after Pentecost. The Armenian Catholic Church commemorates both on 1 July.

Constantine is not recognised officially as a saint in the Latin Church of the Catholic Church, although he had been referred to as piissimi Imperatoris (most pious Emperor) in editions of the Martyrologium Romanum up until the 1956 edition.

Lutheran churches, such as the Lutheran Church – Missouri Synod, commemorate Emperor Constantine alongside his mother, Helena, as saints on 21 May.

During Constantine's lifetime, Praxagoras of Athens and Libanius, pagan authors, showered Constantine with praise, presenting him as a paragon of virtue. His nephew and son-in-law Julian the Apostate, however, wrote the satire Symposium, or the Saturnalia in 361, after the last of his sons died; it denigrated Constantine, calling him inferior to the great pagan emperors, and given over to luxury and greed. Following Julian, Eunapius began – and Zosimus continued – a historiographic tradition that blamed Constantine for weakening the empire through his indulgence to the Christians.

During the Middle Ages, European and Near-East Byzantine writers presented Constantine as an ideal ruler, the standard against which any king or emperor could be measured. The Renaissance rediscovery of anti-Constantinian sources prompted a re-evaluation of his career. German humanist Johannes Leunclavius discovered Zosimus' writings and published a Latin translation in 1576. In its preface, he argues that Zosimus' picture of Constantine offered a more balanced view than that of Eusebius and the Church historians. Cardinal Caesar Baronius criticised Zosimus, favouring Eusebius' account of the Constantinian era. Baronius' Life of Constantine (1588) presents Constantine as the model of a Christian prince. Edward Gibbon aimed to unite the two extremes of Constantinian scholarship in his work The History of the Decline and Fall of the Roman Empire (1776–1789) by contrasting the portraits presented by Eusebius and Zosimus. He presents a noble war hero who transforms into an Oriental despot in his old age, "degenerating into a cruel and dissolute monarch".

Modern interpretations of Constantine's rule begin with Jacob Burckhardt's The Age of Constantine the Great (1853, rev. 1880). Burckhardt's Constantine is a scheming secularist, a politician who manipulates all parties in a quest to secure his own power. Henri Grégoire followed Burckhardt's evaluation of Constantine in the 1930s, suggesting that Constantine developed an interest in Christianity only after witnessing its political usefulness. Grégoire was sceptical of the authenticity of Eusebius's Vita, and postulated a pseudo-Eusebius to assume responsibility for the vision and conversion narratives of that work. Otto Seeck's Geschichte des Untergangs der antiken Welt (1920–1923) and André Piganiol's L'empereur Constantin (1932) go against this historiographic tradition. Seeck presents Constantine as a sincere war hero whose ambiguities were the product of his own naïve inconsistency. Piganiol's Constantine is a philosophical monotheist, a child of his era's religious syncretism. Related histories by Arnold Hugh Martin Jones (Constantine and the Conversion of Europe, 1949) and Ramsay MacMullen (Constantine, 1969) give portraits of a less visionary and more impulsive Constantine.

These later accounts were more willing to present Constantine as a genuine convert to Christianity. Norman H. Baynes began a historiographic tradition with Constantine the Great and the Christian Church (1929) which presents Constantine as a committed Christian, reinforced by Andreas Alföldi's The Conversion of Constantine and Pagan Rome (1948), and Timothy Barnes's Constantine and Eusebius (1981) is the culmination of this trend. Barnes' Constantine experienced a radical conversion which drove him on a personal crusade to convert his empire. Charles Matson Odahl's Constantine and the Christian Empire (2004) takes much the same tack. In spite of Barnes' work, arguments continue over the strength and depth of Constantine's religious conversion. Certain themes in this school reached new extremes in T. G. Elliott's The Christianity of Constantine the Great (1996), which presented Constantine as a committed Christian from early childhood. Paul Veyne's 2007 work Quand notre monde est devenu chrétien holds a similar view which does not speculate on the origin of Constantine's Christian motivation, but presents him as a religious revolutionary who fervently believed that he was meant "to play a providential role in the millenary economy of the salvation of humanity". Peter Heather argues that Constantine's father Constantius was probably a closet Christian who brought his son up in the religion, and that Constantine concealed his adherence so long as it was politically dangerous, gradually "coming out" in stages as he became more dominant.

Latin Christians considered it inappropriate that Constantine was baptised only on his death bed by an unorthodox bishop, and a legend emerged by the early 4th century that Pope Sylvester I had cured the pagan emperor from leprosy. According to this legend, Constantine was baptised and began the construction of a church in the Lateran Basilica. The Donation of Constantine appeared in the 8th century, most likely during the pontificate of Pope Stephen II, in which the freshly converted Constantine gives "the city of Rome and all the provinces, districts, and cities of Italy and the Western regions" to Sylvester and his successors. In the High Middle Ages, this document was used and accepted as the basis for the pope's temporal power, though it was denounced as a forgery by Emperor Otto III and lamented as the root of papal worldliness by Dante Alighieri. Philologist and Catholic priest Lorenzo Valla proved in 1440 that the document was indeed a forgery.

During the medieval period, Britons regarded Constantine as a king of their own people, particularly associating him with Caernarfon in Gwynedd. While some of this is owed to his fame and his proclamation as emperor in Britain, there was also confusion of his family with Magnus Maximus's supposed wife Elen and her son, another Constantine (Welsh: Custennin). In the 12th century Henry of Huntingdon included a passage in his Historia Anglorum that the Emperor Constantine's mother was a Briton, making her the daughter of King Cole of Colchester. Geoffrey of Monmouth expanded this story in his highly fictionalised Historia Regum Britanniae, an account of the supposed Kings of Britain from their Trojan origins to the Anglo-Saxon invasion. According to Geoffrey, Cole was King of the Britons when Constantius, here a senator, came to Britain. Afraid of the Romans, Cole submits to Roman law so long as he retains his kingship. However, he dies only a month later, and Constantius takes the throne himself, marrying Cole's daughter Helena. They have their son Constantine, who succeeds his father as King of Britain before becoming Roman emperor.

Historically, this series of events is extremely improbable. Constantius had already left Helena by the time he left for Britain. Additionally, no earlier source mentions that Helena was born in Britain, let alone that she was a princess. Henry's source for the story is unknown, though it may have been a lost hagiography of Helena.