Constantine the Great: The Years 316-323

The Senate House – Curia – on the Forum Romanum.

During the Roman Republic the Senate had been, from time to time, the most powerful body of the state. During the Principate its power had been greatly reduced, while during the Dominate and the reign of the emperor Diocletianus the Senate had become a marginal factor at best. Constantine more or less resuscitated the Senate after taking Rome at the end of October of 312. Many members of the equestrian order (equites) were promoted to the rank of senator, and towards the end of Constantine’s reign the number of senators had risen from around 600 to almost 1,800.[1] The emperor simply needed the senators for the complex administration of his Empire and also saw the value of close personal ties. Moreover, Constantine proved to be anything but resentful. The former praetorian prefect of the defeated Maxentius, Gaius Rufius Volusianus, was for instance allowed to serve under him as consul (in 314) and praefectus urbi. Perhaps it is in this context that we should view the marriage between Constantine’s Christian half-sister Anastasia (‘Resurrection’) and a senator named Bassianus. This Bassianus would play an important, yet highly shadowy role in the outbreak of war between Constantine and his brother-in-law Licinius.

Constantine vs. Licinius

According to the anonymous author of the Origo Constantini Imperatoris (ca. 390) Constantine had sent his half-brother Julius Constantius to Licinius’ court to ask for permission to make this Bassianus a caesar. The idea was that the senator would administer Italy and serve as some sort of buffer between Constantine and Licinius. Licinius, however, rejected the proposal. It is possible that he believed that Italy was his by right, as it had been granted to him in the past and as recently as 309 he had abortively attempted to take it from Maxentius. In any case, Licinius now got in touch with one Senicio, who was Bassianus’ brother. Senicio then encouraged his brother to take up arms against Constantine, but the plot was discovered and Bassianus was executed (unfortunately we do not know what Anastasia thought of the execution). Constantine now demanded the extradition of Senicio, which Licinius refused. When the latter also ordered the desecration of busts and statues of Constantine in Emona (modern Ljubljana in Slovenia), Constantine had a strong casus belli.[2]

Statue of Constantine II as Caesar, Capitol, Rome.

It is possible that the Origo Constantini Imperatoris tells the official story, i.e. the story that Constantine wanted posterity to know and believe. Perhaps the story is on the whole correct, but it is not inconceivable that the emperor left out certain elements and details. When Constantine put Bassianus forward as caesar, the emperor probably only had one son – Crispus – from his previous relationship with Minervina. Constantine had been married to Fausta for years, but so far she had not borne him any sons. This all changed in February of 316, when Flavius Claudius Constantinus (Constantine II) was born in Arelate in Gaul (modern Arles). The birth of his son had given Constantine a legitimate successor from the line of the Herculii: Fausta’s father was the former emperor Maximianus, and Constantine himself also belonged to the Herculii through his father. This being the case, and Bassianus having been rejected by Licinius as caesar, meant that the senator had outlived his usefulness. It was now essential to get rid of him before Bassianus would himself seize the power that Constantine had promised him. Once Bassianus was out of the way, Licinius became Constantine’s next target.

Constantine gathered an army that, according to the Origo Constantini Imperatoris, was 20,000 men strong. Many of the emperor’s soldiers must have been veterans from his campaigns along the Rhine and in Italy. Constantine marched into the territories of his brother-in-law and reached the city of Cibalae in Pannonia (now Vinkovci in Croatia) without encountering much resistance. According to Zosimus Licinius had established his headquarters here. The city itself was situated on a hill, but Licinius deployed his army of perhaps 35,000 men on the plain in front of it. On 8 October 316, Constantine gave the order to attack. The battle of Cibalae was a fierce battle that was fought from the morning until the evening. Both armies must have suffered heavy casualties. In the end Constantine was victorious and Licinius was forced to retreat to Sirmium (Sremska Mitrovica in Serbia), one of the capitals in his part of the Roman Empire. The Origo Constantini Imperatoris claims he had lost 20,000 men, but this number is no doubt inflated.

The war between Constantine and Licinius in 316-317 (source: Ancient World Mapping Center. “À-la-carte”; CC BY 4.0).

Licinius was not willing to give up yet. In Sirmium he collected his wife Constantia – Constantine’s half-sister – and his son Licinius junior, and then travelled to one of the Dacian provinces (Dacia Aureliana had been split into two separate provinces under Diocletianus). There he had a meeting with the dux Valens, the commander of the border troops or limitanei. The dux probably provided him with fresh troops, and in return Licinius made him an augustus.[3] Constantine had in the meantime captured Cibalae and Sirmium, and subsequently invaded Thrace with his army, where he made his camp at Philippopolis (Plovdiv in Bulgaria). Around the same time Licinius was camping at Hadrianopolis (Edirne in European Turkey). Negotiations between the two brothers-in-law quickly broke down and in January of 317 the two armies clashed again, this time on the plain of Mardia, not far from modern Harmanli in the south of Bulgaria. Thousands of soldiers were killed in the fighting, but the battle ended in a draw.

Licinius (Rijksmuseum van Oudheden, Leiden).

After the battle Constantine marched east, in an attempt to capture Byzantium. He had expected to find Licinius and Valens there, but the two augusti had retreated towards the city of Beroea, also known as Augusta Traiana (modern Stara Zagora in Bulgaria). Beroea was located not east, but north of the battlefield of Mardia, which allowed Licinius and Valens to threaten the rear of Constantine’s army and cut all its supply lines. It was a very clever move by the two men, and it forced Constantine to get back to the negotiating table. Nevertheless, Constantine’s position was apparently still the strongest, as is demonstrated by the peace that Constantine and Licinius subsequently made. The latter lost almost all of his territories in Europe. He was allowed to keep just Thrace, the eastern part of Moesia and Scythia (that is, the area along the Black Sea and at the mouth of the river Danube). The rest of the Balkans, Greece and Macedonia all went to Constantine. Cities such as Corinth, Thessalonica and Philippi, cities where none other than Saint Paul the Apostle had preached, where now under Constantine’s authority.

The peace was formally signed on 1 March 317. It was a date that had been chosen for a reason, as on 1 March of the year 293 Constantine’s father Constantius Chlorus had been appointed caesar. Constantine, who had taken up residence in Serdica (Sofia), now appointed his approximately seventeen-year-old son Crispus and Crispus’ one-year-old half-brother Constantine II caesares. Licinius followed suit by appointing his son Licinius junior, who was twenty months old, caesar as well. Valens had now lost his value for Licinius. The former augustus was therefore executed.[4]

The long run-up to the next war

The newly appointed caesares were not junior emperors as intended under the Tetrarchy. Constantine had broken with that system of government for good. There was only one true emperor in het whole Roman Empire and that was Constantine himself, who for the moment still had to tolerate Licinius as a severely weakened rival. Of the new caesares only Crispus was old enough to be given positions in the army and in civil administration, so around 318 Constantine sent him to Augusta Treverorum (Trier). All of Northern Gaul and Britannia – the dioceses Galliae and Britanniae – were put under his authority. In 320 the young men would distinguish himself with a splendid victory over the Alemanni. For the moment Constantine II was still an infant. In Augustus of 317 Fausta gave birth to his brother Flavius Julius Constantius. Constantius II – as he became known later – quickly became his father’s favourite. Lastly, in 322 or 323 Flavius Julius Constans was born, so Constantine now had one big happy family. Of course in the highly patriarchal Roman Empire family happiness was almost entirely dependent on the birth of sons. Constantine and Fausta also had two daughters, Constantina and Helena, but we do not even know their years of birth.

Statue of the emperor Constantine, San Giovanni in Laterano.

That Constantine was aiming for a new war against Licinius in the near future was crystal clear from the cities he chose as his residences between 317 and 324. Sirmium, Serdica and Thessalonica were all close to the remaining territories of his brother-in-law in Europe. For the moment Constantine’s chief occupation was affairs of religion. In 317 the first Christian consul had taken up office in Rome, one Ovinius Gallicanus. He would soon be followed by others, including scions of the influential gens Anicia. In the years discussed here Constantine took several notable measures that were evidently pro-Christian. Bishops and other members of the clergy were granted a number of tax exemptions, and from now on the emancipation of a slave by a bishop had the same legal effect as an emancipation effected before a secular magistrate. Bishops were furthermore granted the power to act as judges in civil cases.[5]

An extremely important decision was the law enacted in March of 321 that made Sundays holidays. The law is sometimes interpreted as a gesture towards the cult of Sol Invictus. It is true that the day was mentioned in Latin as the dies solis and not the dies domenica (‘day of the Lord’), a term that Christians in the Latin west commonly used. But that does not explain why the measure was not taken half a century earlier, when the cult of Sol Invictus was at its peak under the emperor Aurelianus. When the law of 321 was enacted, Sol had not appeared on Constantine’s bronze coins for a full three years. The Sunday rest seems to have been especially beneficial to the Christians. Christian soldiers (still a small minority in the Roman army) could now go to church on Sundays, courts closed their doors and only the (numerous!) farmers continued their work on the dies solis. If the account given by Eusebius of Caesarea is reliable, then Constantine at some point even required his non-Christian soldiers – so the vast majority – to recite a prayer on Sundays in which the Christian god was recognised as monon theon, ‘only God’.[6]

Arch of Constantine in Rome.

At the same time Constantine did not necessarily reject violence against Christians that held heretical views. In North Africa bishop Caecilianus of Carthage, who had the support of the emperor, as of 317 began suppressing the Donatists. For this he made use of the Roman army. People were killed, and the Donatists saw these victims as martyrs. The fact that a couple of years later Constantine tried to reconcile the official church and the schismatics in North Africa was no doubt related to the imminent war against Licinius. For the Donatists, Constantine was basically just a persecutor of Christians, much like Diocletianus, Galerius and Maximinus Daza had been before him. Constantine for his part needed to portray Licinius as a persecutor of Christians, so as to justify the upcoming war against his brother-in-law and – after having won it – win the hearts and minds of the sizeable Christian communities in the east of the Roman Empire. It is quite likely that in all of these religious affairs Constantine consulted a number of permanent advisors, including his confidant, bishop Ossius of Corduba.


As was already mentioned, Constantine had an interest in framing Licinius as a persecutor of Christians. In an account that can hardly be called impartial, the Christian author Eusebius gives a list of all the horrible things that Licinius allegedly did to the Christians in the Roman east.[7] Although Eusebius was exaggerating, there can be no doubt that from ca. 320 Licinius indeed began displaying ever more hostility towards the Christians in his part of the Roman Empire. He for instance fired civil servants and court officials that refused to sacrifice to the “demons” (the traditional gods). Eusebius’ accusations of the destruction of churches and the arrest of several bishops in Amasea in Pontus do not seem to be entirely fictional, although we may certainly question the cruel executions that our author has included.[8] Eusebius in fact does not even mention the name of a single martyr. Nevertheless, the situation in the east must have been tense. Licinius’ authority was disputed and Christian communities were torn by doctrinarian strive. Around the year 319 an influential priest named Arius had announced that Christ had been created by God and must therefore be subordinate to Him. This view had greatly angered patriarch Alexander I of Alexandria, who claimed that God and Christ were of the same substance (“consubstantial”). Arius was ultimately excommunicated, but the “Arian question” would soon give Constantine a headache.

Constantine Augustus.

Meanwhile, Constantine was mostly busy trying to provoke a war that would bring the entire Roman Empire under his control. In the autumn of 322, during a campaign against the Sarmatians, he accidentally or deliberately entered the territories along the Danube that were part of Licinius’ foothold in Europe. The latter decided not to respond, and in 323 Constantine repeated his actions during a campaign against the Goths. A definite break between the two brothers-in-law had now become inevitable. As of 321 Licinius had stopped recognising the consuls nominated by Constantine and now the two men began preparing for armed conflict. Licinius gathered an army in Thrace and Constantine – who now held the titles of Sarmaticus maximus and Gothicus – did the same in Thessalonica. Moreover, both emperors constructed or assembled large fleets. Constantine recalled his eldest son Crispus from Gaul and appointed him fleet commander. Next year it would be decided who would rule over the entire Roman Empire.


Primary sources

Secondary sources

  • Adrian Goldsworthy, The Fall of the West, p. 178 and 187-189;
  • Henk Singor, Constantijn, p. 312-345;
  • Timothy Venning, A Chronology of the Roman Empire, p. 649-651.


[1] Henk Singor, Constantijn, p. 277.

[2] Origo Constantini Imperatoris 5.14-15.

[3] A caesar according to the sources, but Valens’ coins make clear that he was an augustus.

[4] The Origo Constantini Imperatoris 5.18 claims that he was allowed to live, but according to the Epitome de Caesaribus 40.9 and according to Zosimus Licinius had him executed.

[5] For a full discussion of Constantine’s measures, see Henk Singor, Constantijn, p. 320-321.

[6] Eusebius, Vita Constantini, Book 4.19-20.

[7] Eusebius, Vita Constantini, Book 1.49-56.

[8] Eusebius, Vita Constantini, Book 2.1-2.

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