Born in Naissus, in Dardania within Moesia Superior (now Niš, Serbia), Constantine was the son of Flavius Constantius, a Roman army officer of Illyrian origin who would become one of the four emperors of the Tetrarchy.

[15] The fullest secular life of Constantine is the anonymous Origo Constantini,[16] a work of uncertain date[17] which focuses on military and political events to the neglect of cultural and religious matters.

[18] Lactantius' De mortibus persecutorum, a political Christian pamphlet on the reigns of Diocletian and the Tetrarchy, provides valuable but tendentious detail on Constantine's predecessors and early life.

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.

Over the spring and summer of 307, he had left Gaul for Britain to avoid any involvement in the Italian turmoil;[110] now, instead of giving Maxentius military aid, he sent his troops against Germanic tribes along the Rhine.

[122] 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.

[130] 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.

His early support dissolved in the wake of heightened tax rates and depressed trade; riots broke out in Rome and Carthage;[138] and Domitius Alexander was able to briefly usurp his authority in Africa.

He ordered all bridges across the Tiber cut, reportedly on the counsel of the gods,[166] and left the rest of central Italy undefended; Constantine secured that region's support without challenge.

"[175] Eusebius describes a vision that Constantine had while marching at midday in which "he saw with his own eyes the trophy of a cross of light in the heavens, above the sun, and bearing the inscription, In Hoc Signo Vinces" ("In this sign thou shalt conquer").

[176] In Eusebius's account, Constantine had a dream the following night in which Christ appeared with the same heavenly sign and told him to make an army standard in the form of the labarum.

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[226] as well as being able to monitor shipping traffic between the Black Sea and the Mediterranean.

[230] 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.

[246] He supported the Church financially, built basilicas, granted privileges to clergy (such as exemption from certain taxes), promoted Christians to high office, and returned property confiscated during the long period of persecution.

A triumphal arch was built in 315 to celebrate his victory in the Battle of the Milvian Bridge which was decorated with images of the goddess Victoria, and sacrifices were made to pagan gods at its dedication, including Apollo, Diana, and Hercules.

Constantine gained the support of the old nobility with this,[265] as the Senate was allowed to elect praetors and quaestors in place of the usual practice of the emperors directly creating magistrates (adlectio).

A popular myth arose, modified to allude to the Hippolytus–Phaedra legend, with the suggestion that Constantine killed Crispus and Fausta for their immoralities;[280] the largely fictional Passion of Artemius explicitly makes this connection.

[302] Following his death, his body was transferred to Constantinople and buried in the Church of the Holy Apostles,[303] in a porphyry sarcophagus that was described in the 10th century by Constantine VII Porphyrogenitus in the De Ceremoniis.

[306] A number of relatives were killed by followers of Constantius, notably Constantine's nephews Dalmatius (who held the rank of caesar) and Hannibalianus, presumably to eliminate possible contenders to an already complicated succession.

[308] 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).

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.

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.

[333] 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.

[344] 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".

[346] 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.

[349] In the High Middle Ages,[350][351] 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[352] and lamented as the root of papal worldliness by Dante Alighieri.

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.

[355] 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.