Editing Constantine the Great (section)

=== Civil wars ===
{{See also|Civil wars of the Tetrarchy}}

==== War against Maxentius ====
{{Campaignbox Constantine Wars}}
By the middle of 310 Galerius had become too ill to involve himself in imperial politics.<ref>Lactantius, ''De Mortibus Persecutorum'' 31–35; Eusebius, ''Historia Ecclesiastica'' 8.16; Elliott, ''Christianity of Constantine'', 43; Lenski, "Reign of Constantine" (CC), 68; Odahl, 95–96, 316.</ref> 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.<ref>Lactantius, ''De Mortibus Persecutorum'' 34; Eusebius, ''Historia Ecclesiastica'' 8.17; Barnes, ''Constantine and Eusebius'', 304; Jones, 66.</ref>

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."<ref>{{Cite book |last=Eusebius |title=The History of the Church |publisher=Penguin Classics |year=1965 |isbn=0140445358 |pages=278}}</ref>

Galerius died soon after the edict's proclamation,<ref>Barnes, ''Constantine and Eusebius'', 39; Elliott, ''Christianity of Constantine'', 43–44; Lenski, "Reign of Constantine" (CC), 68; Odahl, 95–96.</ref> destroying what little remained of the Tetrarchy.<ref>Barnes, ''Constantine and Eusebius'', 41; Elliott, ''Christianity of Constantine'', 45; Lenski, "Reign of Constantine" (CC), 69; Odahl, 96.</ref> Maximinus mobilised against Licinius and seized [[Anatolia|Asia Minor]]. A hasty peace was signed on a boat in the middle of the [[Bosporus|Bosphorus]].<ref>Barnes, ''Constantine and Eusebius'', 39–40; Elliott, ''Christianity of Constantine'', 44; Odahl, 96.</ref> While Constantine toured Britain and Gaul, Maxentius prepared for war.<ref>Odahl, 96.</ref> He fortified northern Italy and strengthened his support in the Christian community by allowing it to elect [[Pope Eusebius|Eusebius]] as [[diocese of Rome|bishop of Rome]].<ref>Barnes, ''Constantine and Eusebius'', 38; Odahl, 96.</ref>[[File:Dame-Schmuckkasten-Trier.jpg|thumb|left|A Roman fresco in [[Trier]], Germany, possibly depicting [[Flavia Julia Constantia|Constantia]]<ref>{{Cite book |last=Hillner |first=Julia |date=2017 |title=Constantia |chapter=Constantia, half-sister of Constantine and wife of Licinius |url=https://oxfordre.com/display/10.1093/acrefore/9780199381135.001.0001/acrefore-9780199381135-e-8065 |series=Oxford Research Encyclopedia of Classics |doi=10.1093/acrefore/9780199381135.013.8065 |isbn=978-0-19-938113-5}}</ref>]]
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]];<ref>Barnes, ''Constantine and Eusebius'', 37; Curran, 66; Lenski, "Reign of Constantine" (CC), 68; MacMullen, ''Constantine'', 62.</ref> and [[Domitius Alexander]] was able to briefly usurp his authority in Africa.<ref name="leohak">Barnes, ''Constantine and Eusebius'', 37.</ref> By 312, he was a man barely tolerated, not one actively supported,<ref>Barnes, ''Constantine and Eusebius'', 37–39.</ref> even among Christian Italians.<ref>Barnes, ''Constantine and Eusebius'', 38–39; MacMullen, ''Constantine'', 62.</ref> 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".<ref>Barnes, ''Constantine and Eusebius'', 40; Curran, 66.</ref> To prevent Maxentius from forming an alliance against him with Licinius,<ref>Barnes, ''Constantine and Eusebius'', 41.</ref> Constantine forged his own alliance with Licinius over the winter of 311–312 and offered him his sister [[Flavia Julia Constantia|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.<ref>Barnes, ''Constantine and Eusebius'', 41; Elliott, ''Christianity of Constantine'', 44–45; Lenski, "Reign of Constantine" (CC), 69; Odahl, 96.</ref> According to Eusebius, inter-regional travel became impossible, and there was military buildup everywhere. There was "not a place where people were not expecting the onset of hostilities every day".<ref>Eusebius, ''Historia Ecclesiastica'' 8.15.1–2, qtd. and tr. in MacMullen, ''Constantine'', 65.</ref>

[[File:Battle of Constantine and Maxentius (detail-of-fresco-in-Vatican-Stanze) c1650 by Lazzaro Baldi after Giulio Romano at the University of Edinburgh.jpg|thumb|''Battle of Constantine and Maxentius'' (detail of part of a fresco by [[Giulio Romano (painter)|Giulio Romano]] in the Hall of Constantine in the [[Raphael Rooms]] in the [[Vatican Museums|Vatican]]), copy c. 1650 by [[Lazzaro Baldi]], now at the University of Edinburgh]]

Constantine's advisers and generals cautioned against preemptive attack on Maxentius;<ref>Barnes, ''Constantine and Eusebius'', 41; MacMullen, ''Constantine'', 71.</ref> even his soothsayers recommended against it, stating that the sacrifices had produced unfavourable omens.<ref>''Panegyrici Latini'' 12(9)2.5; Curran, 67.</ref> Constantine, with a spirit that left a deep impression on his followers, inspiring some to believe that he had some form of supernatural guidance,<ref>Curran, 67.</ref> ignored all these cautions.<ref>MacMullen, ''Constantine'', 70–71.</ref> Early in the spring of 312,<ref name="esyyqc">Barnes, ''Constantine and Eusebius'', 41; Odahl, 101.</ref> Constantine crossed the [[Cottian Alps]] with a quarter of his army, a force numbering about 40,000.<ref>''Panegyrici Latini'' 12(9)5.1–3; Barnes, ''Constantine and Eusebius'', 41; MacMullen, ''Constantine'', 71; Odahl, 101.</ref> The first town his army encountered was ''Segusium'' ([[Susa, Piedmont|Susa]], Italy), a heavily fortified town that shut its gates to him. Constantine ordered his men to set fire to its gates and scale its walls. He took the town quickly. Constantine ordered his troops not to loot the town and advanced into northern Italy.<ref name="esyyqc" />

At the approach to the west of the important city of Augusta Taurinorum ([[Turin]], Italy), Constantine met a large force of heavily armed Maxentian cavalry.<ref>Barnes, ''Constantine and Eusebius'', 41; Jones, 70; MacMullen, ''Constantine'', 71; Odahl, 101–02.</ref> In the ensuing [[Battle of Turin (312)|Battle of Turin]] Constantine's army encircled Maxentius' cavalry, [[Flanking maneuver|flanked]] them with his own cavalry, and dismounted them with blows from his soldiers' iron-tipped clubs. Constantine's armies emerged victorious.<ref>''Panegyrici Latini'' 12(9)5–6; 4(10)21–24; Jones, 70–71; MacMullen, ''Constantine'', 71; Odahl, 102, 317–18.</ref> Turin refused to give refuge to Maxentius' retreating forces, opening its gates to Constantine instead.<ref>Barnes, ''Constantine and Eusebius'', 41; Jones, 71; Odahl, 102.</ref> Other cities of the north Italian plain sent Constantine embassies of congratulation for his victory. He moved on to Milan, where he was met with open gates and jubilant rejoicing. Constantine rested his army in Milan until mid-summer 312, when he moved on to Brixia ([[Brescia]]).<ref>Barnes, ''Constantine and Eusebius'', 41–42; Odahl, 103.</ref>

Brescia's army was easily dispersed,<ref>Barnes, ''Constantine and Eusebius'', 42; Jones, 71; MacMullen, ''Constantine'', 71; Odahl, 103.</ref> and Constantine quickly advanced to [[Verona]] where a large Maxentian force was camped.<ref>Jones, 71; MacMullen, ''Constantine'', 71; Odahl, 103.</ref> [[Ruricius Pompeianus]], general of the Veronese forces and Maxentius' praetorian prefect,<ref>Jones, 71; Odahl, 103.</ref> was in a strong defensive position since the town was surrounded on three sides by the [[Adige]]. Constantine sent a small force north of the town in an attempt to cross the river unnoticed. Ruricius sent a large detachment to counter Constantine's expeditionary force but was defeated. Constantine's forces successfully surrounded the town and laid siege.<ref>Barnes, ''Constantine and Eusebius'', 42; Jones, 71; Odahl, 103.</ref> Ruricius gave Constantine the slip and returned with a larger force to oppose Constantine. Constantine refused to let up on the siege and sent only a small force to oppose him. In the desperately fought [[Battle of Verona (312)|encounter]] that followed, Ruricius was killed and his army destroyed.<ref>Barnes, ''Constantine and Eusebius'', 42; Jones, 71; Odahl, 103–04.</ref> Verona surrendered soon afterwards, followed by [[Aquileia]],<ref>Barnes, ''Constantine and Eusebius'', 42; Jones, 71; Lenski, "Reign of Constantine" (CC), 69; MacMullen, ''Constantine'', 71; Odahl, 104.</ref> Mutina ([[Modena]]),<ref>Jones, 71; MacMullen, ''Constantine'', 71.</ref> and [[Ravenna]].<ref>MacMullen, ''Constantine'', 71.</ref> The road to Rome was now wide open to Constantine.<ref>Barnes, ''Constantine and Eusebius'', 42; Curran, 67; Jones, 71.</ref>

[[File:Ponte Milvio-side view-antmoose.jpg|thumb|upright=1.8|right|The Milvian Bridge ([[Ponte Milvio]]) over the [[Tiber|River Tiber]], north of Rome, where Constantine and Maxentius fought in the [[Battle of the Milvian Bridge]]]]
Maxentius prepared for the same type of war he had waged against Severus and Galerius: he occupied Rome and prepared for a siege.<ref>Barnes, ''Constantine and Eusebius'', 42; Jones, 71; Odahl, 105.</ref> He still controlled Rome's [[Praetorian Guard]], was well-stocked with African grain, and was surrounded on all sides by the seemingly impregnable [[Aurelian Walls]]. He ordered all bridges across the [[Tiber]] cut, reportedly on the counsel of the gods,<ref>Jones, 71.</ref> and left the rest of central Italy undefended; Constantine secured that region's support without challenge.<ref>Odahl, 104.</ref> Constantine progressed slowly<ref name="BC42">Barnes, ''Constantine and Eusebius'', 42.</ref> along the ''[[Via Flaminia]]'',<ref>MacMullen, ''Constantine'', 72; Odahl, 107.</ref> allowing the weakness of Maxentius to draw his regime further into turmoil.<ref name="BC42" /> Maxentius' support continued to weaken: at chariot races on 27 October, the crowd openly taunted Maxentius, shouting that Constantine was invincible.<ref>Barnes, ''Constantine and Eusebius'', 42; Curran, 67; Jones, 71–72; Odahl, 107–8.</ref> Maxentius, no longer certain that he would emerge from a siege victorious, built a temporary boat bridge across the Tiber in preparation for a field battle against Constantine.<ref>Barnes, ''Constantine and Eusebius'', 42–43; MacMullen, ''Constantine'', 78; Odahl, 108.</ref> On 28 October 312, the sixth anniversary of his reign, he approached the keepers of the [[Sibylline Books]] for guidance. The keepers prophesied that, on that very day, "the enemy of the Romans" would die. Maxentius advanced north to meet Constantine in battle.<ref>Lactantius, ''De Mortibus Persecutorum'' 44.8; Barnes, ''Constantine and Eusebius'', 43; Curran, 67; Jones, 72; Odahl, 108.</ref>

==== Constantine adopts the Greek letters Chi Rho for Christ's initials ====
{{See also|Chi Rho}}
{{Main|Battle of the Milvian Bridge}}
{{Further|Ponte Milvio}}
[[File:Konstantinsmedaillon.jpg|thumb|Silver [[medallion]] of 315; Constantine with a [[chi-rho]] symbol as the crest of his [[Helmet of Constantine|helmet]]]]
Maxentius' forces were still twice the size of Constantine's, and he organised them in long lines facing the battle plain with their backs to the river.<ref name="bvubfs">Odahl, 108.</ref> Constantine's army arrived on the field bearing unfamiliar symbols on their standards and their shields.<ref>Barnes, ''Constantine and Eusebius'', 43; Digeser, 122; Jones, 72; Odahl, 106.</ref> According to Lactantius "Constantine was directed in a dream to cause the heavenly sign to be delineated on the shields of his soldiers, and so to proceed to battle. He did as he had been commanded, and he marked on their shields the letter Χ, with a perpendicular line drawn through it and turned round thus at the top, being the cipher of Christ. Having this sign (☧), his troops stood to arms."<ref>Lactantius, ''De Mortibus Persecutorum'' 44.4–6, tr. J.L. Creed, ''Lactantius: De Mortibus Persecutorum'' (Oxford: Oxford University Press, 1984), qtd. in Lenski, "Reign of Constantine" (CC), 71.</ref> 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").<ref>Eusebius, ''Vita Constantini'' 1.28, tr. Odahl, 105. Barnes, ''Constantine and Eusebius'', 43; Drake, "Impact of Constantine on Christianity" (CC), 113; Odahl, 105.</ref> In Eusebius' 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]]''.<ref>Eusebius, ''Vita Constantini'' 1.27–29; Barnes, ''Constantine and Eusebius'', 43, 306; Odahl, 105–06, 319–20.</ref> Eusebius is vague about when and where these events took place,<ref>Drake, "Impact of Constantine on Christianity" (CC), 113.</ref> but it enters his narrative before the war begins against Maxentius.<ref>Cameron and Hall, 208.</ref> He describes the sign as [[Chi (letter)|Chi]] (Χ) traversed by [[Rho]] (Ρ) to form ☧, representing the first two letters of the Greek word {{lang|grc|ΧΡΙΣΤΟΣ}} (Christos).<ref>Barnes, ''Constantine and Eusebius'', 306; MacMullen, ''Constantine'', 73; Odahl, 319.</ref><ref>Cameron and Hall, 206–07; Drake, "Impact of Constantine on Christianity" (CC), 114; Nicholson, 311.</ref> A medallion was issued at [[Pavia|Ticinum]] in 315 which shows Constantine [[Helmet of Constantine|wearing a helmet]] emblazoned with the ''[[Chi Rho]]'',<ref>Lenski, "Reign of Constantine" (CC), 71, citing ''Roman Imperial Coinage'' 7 Ticinum 36.</ref> and coins issued at Siscia in 317/318 repeat the image.<ref>R. Ross Holloway, ''Constantine and Rome'' (New Haven: Yale University Press, 2004), 3, citing Kraft, "Das Silbermedaillon Constantins des Grosses mit dem Christusmonogram auf dem Helm", ''Jahrbuch für Numismatik und Geldgeschichte'' 5–6 (1954/55): 151–78.</ref> The figure was otherwise rare and is uncommon in imperial iconography and propaganda before the 320s.<ref>Lenski, "Reign of Constantine" (CC), 71.</ref> It was not completely unknown, however, being an abbreviation of the Greek word chrēston (good), having previously appeared on the coins of [[Ptolemy III Euergetes]] in the 3rd century BC. Following Constantine, centuries of Christians invoked the miraculous or the supernatural when justifying or describing their warfare.<ref>{{Cite book |title=Miracles, political authority and violence in medieval and early modern history |date=2022 |publisher=Routledge, Taylor & Francis Group |isbn=978-0-367-76728-0 |editor-last=Rowley |editor-first=Matthew |series=Themes in medieval and early modern history |location=London New York |editor-last2=Hodgson |editor-first2=Natasha R.}}</ref>

Constantine deployed his own forces along the whole length of Maxentius' line. He ordered his cavalry to charge, and they broke Maxentius' cavalry. He then sent his infantry against Maxentius' infantry, pushing many into the Tiber where they were slaughtered and drowned.<ref name="bvubfs" /> The battle was brief,<ref>Barnes, ''Constantine and Eusebius'', 43; Curran, 68.</ref> and Maxentius' troops were broken before the first charge.<ref>MacMullen, ''Constantine'', 78.</ref> His horse guards and praetorians initially held their position, but they broke under the force of a Constantinian cavalry charge; they also broke ranks and fled to the river. Maxentius rode with them and attempted to cross the bridge of boats ([[Ponte Milvio]]), but he was pushed into the Tiber and drowned by the mass of his fleeing soldiers.<ref>Barnes, ''Constantine and Eusebius'', 43; Curran, 68; Lenski, "Reign of Constantine" (CC), 70; MacMullen, ''Constantine'', 78; Odahl, 108.</ref>

==== In Rome ====
[[File:0 Gaius Flavius Valerius Constantinus, Palatino.jpg|thumb|Head of a [[bronze colossus of Constantine]], now in the [[Capitoline Museums]]<ref>[http://www.museicapitolini.org/it/percorsi/percorsi_per_sale/museo_del_palazzo_dei_conservatori/esedra_di_marco_aurelio/statua_colossale_bronzea_di_costantino_testa Head of the bronze colossus], Capitoline Museums</ref>
<!-- this is a difference stone head: <ref>{{cite web |url=http://www.metmuseum.org/art/collection/search/252884 |title=Portrait Head of the Emperor Constantine, Metropolitan Museum of Art, 26.229 |publisher=Metmuseum.org |date=28 June 2017 |access-date=28 June 2017}}</ref>-->
]]
Constantine entered Rome on 29 October 312{{sfn|Barnes|1981|loc=[https://books.google.com/books?id=LGDjJK-JeSwC&pg=PA44 p.&nbsp;44]}}<ref>MacMullen, ''Constantine'', 81; Odahl, 108.</ref> and staged a grand ''adventus'' in the city which was met with jubilation.<ref>Cameron, 93; Curran, 71–74; Odahl, 110.</ref> Maxentius' body was fished out of the Tiber and decapitated, and his head was paraded through the streets for all to see.<ref>Barnes, ''Constantine and Eusebius'', 44; Curran, 72; Jones, 72; Lenski, "Reign of Constantine" (CC), 70; MacMullen, ''Constantine'', 78; Odahl, 108.</ref> After the ceremonies, the disembodied head was sent to Carthage, and Carthage offered no further resistance.<ref>Barnes, ''Constantine and Eusebius'', 44–45.</ref> Unlike his predecessors, Constantine neglected to make the trip to the [[Capitoline Hill]] and perform customary sacrifices at the [[Temple of Jupiter Optimus Maximus|Temple of Jupiter]].<ref>Barnes, ''Constantine and Eusebius'', 44; MacMullen, ''Constantine'', 81; Odahl, 111. Cf. also Curran, 72–75.</ref> However, he did visit the Senatorial [[Curia Julia]],<ref>Barnes, ''Constantine and Eusebius'', 45; Curran, 72; MacMullen, ''Constantine'', 81; Odahl, 109.</ref> and he promised to restore its ancestral privileges and give it a secure role in his reformed government; there would be no revenge against Maxentius' supporters.<ref>Barnes, ''Constantine and Eusebius'', 45–46; Odahl, 109.</ref> In response, the [[Roman Senate|Senate]] decreed him "title of the first name", which meant that his name would be listed first in all official documents,<ref>Barnes, ''Constantine and Eusebius'', 46; Odahl, 109.</ref> and they acclaimed him as "the greatest augustus".<ref>Barnes, ''Constantine and Eusebius'', 46.</ref> He issued decrees returning property that was lost under Maxentius, recalling political exiles, and releasing Maxentius' imprisoned opponents.<ref>Barnes, ''Constantine and Eusebius'', 44.</ref>

An extensive propaganda campaign followed, during which Maxentius' image was purged from all public places. He was written up as a "tyrant" and set against an idealised image of Constantine the "liberator". Eusebius is the best representative of this strand of Constantinian propaganda.<ref>Barnes, ''Constantine and Eusebius'', 45–47; Cameron, 93; Curran, 76–77; Lenski, "Reign of Constantine" (CC), 70.</ref> Maxentius' rescripts were declared invalid, and the honours that he had granted to leaders of the Senate were also invalidated.<ref name="Barnes, CE, 45">Barnes, ''Constantine and Eusebius'', 45.</ref> Constantine also attempted to remove Maxentius' influence on Rome's urban landscape. All structures built by him were rededicated to Constantine, including the [[Santi Cosma e Damiano, Rome#History|Temple of Romulus]] and the [[Basilica of Maxentius]].<ref>Curran, 80–83.</ref> At the focal point of the basilica, a stone statue was erected of Constantine holding the Christian ''labarum'' in its hand. Its inscription bore the message which the statue illustrated: "By this sign, Constantine had freed Rome from the yoke of the tyrant."<ref>Barnes, ''Constantine and Eusebius'', 47.</ref>

Constantine also sought to upstage Maxentius' achievements. For example, the [[Circus Maximus]] was redeveloped so that its seating capacity was 25 times larger than that of Maxentius' racing complex on the [[Appian Way|Via Appia]].<ref>Curran, 83–85.</ref> Maxentius' strongest military supporters were neutralised when Constantine disbanded the Praetorian Guard and [[Equites singulares Augusti|Imperial Horse Guard]].<ref>Barnes, ''Constantine and Eusebius'', 45; Curran, 76; Odahl, 109.</ref> The tombstones of the Imperial Horse Guard were ground up and used in a basilica on the [[Via Labicana]],<ref>Curran, 101.</ref> and their former base was redeveloped into the [[Archbasilica of Saint John Lateran|Lateran Basilica]] on 9 November 312—barely two weeks after Constantine captured the city.<ref>Krautheimer, ''Corpus Basilicarum Christianarum Romanorum'', 5.90, cited in Curran, 93–96.</ref> The [[Legio II Parthica]] was removed from [[Albano Laziale]],<ref name="Barnes, CE, 45" /> and the remainder of Maxentius' armies were sent to do frontier duty on the Rhine.<ref>Odahl, 109.</ref>

==== Wars against Licinius ====
[[File:Aureus of Licinius.png|thumb|upright=1.2|Gold [[aureus]] of the emperor [[Licinius]]]]
In the following years, Constantine gradually consolidated his military superiority over his rivals in the crumbling Tetrarchy. In 313, he met Licinius in Milan to secure their alliance by the marriage of Licinius and Constantine's half-sister Constantia. During this meeting, the emperors agreed on the so-called [[Edict of Milan]],<ref>The term is a misnomer as the act of Milan was not an edict, while the subsequent edicts by Licinius—of which the edicts to the provinces of Bythinia and Palestine are recorded by Lactantius and Eusebius, respectively—were not issued in Milan.</ref> officially granting full tolerance to Christianity and all religions in the empire.<ref>Pohlsander, ''Emperor Constantine'', 25.</ref> The document had special benefits for Christians, legalising their religion and granting them restoration for all property seized during Diocletian's persecution. It repudiates past methods of religious coercion and used only general terms to refer to the divine sphere—"Divinity" and "Supreme Divinity", ''summa divinitas''.<ref>Drake, "Impact", 121–23.</ref> The conference was cut short, however, when news reached Licinius that his rival [[Maximinus Daza|Maximinus]] had crossed the Bosporus and invaded European territory. Licinius departed and eventually defeated Maximinus, gaining control over the entire eastern half of the Roman Empire. Relations between the two remaining emperors deteriorated, as Constantine suffered an assassination attempt at the hands of a character that Licinius wanted elevated to the rank of Caesar;<ref name="ReferenceA">Carrié & Rousselle, ''L'Empire Romain'', 229.</ref> Licinius, for his part, had Constantine's statues in Emona destroyed.<ref>Byfield, Ted, ed. ''The Christians: Their First Two Thousand Years''. vol. III. p. 148. {{cite web |url=http://www.christianhistoryproject.org/to-the-constantine-era/constantine |title=The sign in the sky that changed history |access-date=5 February 2016 |url-status=dead |archive-url=https://web.archive.org/web/20160119071854/http://www.christianhistoryproject.org/to-the-constantine-era/constantine/ |archive-date=19 January 2016}}</ref> In either 314 or 316 the two augusti fought against one another at the [[Battle of Cibalae]], with Constantine being victorious. They clashed again at the [[Battle of Mardia]] in 317 and agreed to a settlement in which Constantine's sons [[Crispus]] and [[Constantine II (emperor)|Constantine II]], and Licinius' son [[Licinius II|Licinius Junior]] were made ''caesars''.<ref>Pohlsander, ''Emperor Constantine'', pp. 38–39.</ref>  After this arrangement, Constantine ruled the dioceses of Pannonia and Macedonia and took residence at [[Sirmium]], whence he could wage war on the Goths and Sarmatians in 322, and on the Goths in 323, defeating and killing their leader [[Rausimod]].<ref name="ReferenceA" />

In 320 Licinius allegedly reneged on the religious freedom promised by the Edict of Milan and began to oppress Christians anew,<ref>Pohlsander, ''Emperor Constantine'', pp. 41–42.</ref> generally without bloodshed, but resorting to confiscations and sacking of Christian office-holders.<ref>Carrié & Rousselle, ''L'Empire Romain'', pp. 229–30.</ref> Although this characterisation of Licinius as anti-Christian is somewhat doubtful, the fact is that he seems to have been far less open in his support of Christianity than Constantine. Therefore, Licinius was prone to see the Church as a force more loyal to Constantine than to the Imperial system in general,<ref>Timothy E. Gregory, ''A History of Byzantium''. Chichester: John Wiley & Sons, 2010, {{ISBN|978-1-4051-8471-7}}, p. 54.</ref> as the explanation offered by the Church historian [[Sozomen]].<ref>Philip Schaff, ed., ''Nicene and Post-nicene Fathers: Second Series''. New York: Cosimo, 2007, {{ISBN|978-1-60206-508-6}}, p. 418, footnote 6.</ref>

This dubious arrangement eventually became a challenge to Constantine in the West, climaxing in the great civil war of 324. Constantine's Christian eulogists present the war as a battle between Christianity and paganism; Licinius, aided by Gothic mercenaries, represented the past and ancient paganism, while Constantine and his [[Franks]] marched under the standard of the ''labarum''.{{citation needed|date=August 2021}} Outnumbered but fired by their zeal, Constantine's army emerged victorious in the [[Battle of Adrianople (324)|Battle of Adrianople]]. Licinius fled across the Bosphorus and appointed [[Martinian (emperor)|Martinian]], his ''[[magister officiorum]]'', as nominal augustus in the West, but Constantine next won the [[Battle of the Hellespont]] and finally the [[Battle of Chrysopolis]] on 18 September 324.<ref>Pohlsander, ''Emperor Constantine'', 42–43.</ref> Licinius and Martinian surrendered to Constantine at ''Nicomedia'' on the promise their lives would be spared: they were sent to live as private citizens in Thessalonica and Cappadocia respectively, but in 325 Constantine accused Licinius of plotting against him and had them both arrested and hanged; Licinius' son (the son of Constantine's half-sister) was killed in 326.<ref>Scarre, ''Chronicle of the Roman Emperors'', 215.</ref> Thus Constantine became the sole emperor of the Roman Empire.<ref name="macmullen">MacMullen, ''Constantine''.</ref>