Flavius Valerius Constantius (c. 250 – 25 July 306), also calledConstantius I, was aRoman emperor from 305 to 306. He was one of the four original members of theTetrarchy established byDiocletian, first serving ascaesar from 293 to 305 and then ruling asaugustus until his death. Constantius was also father ofConstantine the Great, the first Christian emperor of Rome. The nickname "Chlorus" (Ancient Greek:Χλωρός,lit. 'the Pale') was first popularized byByzantine-era historians and not used during the emperor's lifetime.

Constantius Chlorus
Portrait usually identified with that of Constantius,Ny Carlsberg Glyptotek[1]
Roman emperor (in theWest)
Augustus	1 May 305 – 25 July 306 (withGalerius in theEast)
Predecessor	Maximian
Successor	Severus II(officially) Constantine I(rebelled)
Caesar	1 March 293 – 1 May 305
Born	Flavius Constantius 31 Marchc. 250 Naissus,Moesia Superior
Died	25 July 306 (agedc. 56) Eboracum,Roman Britain
Spouse	Helena (disputed) andTheodora
Issue among others	Constantine the Great Flavius Dalmatius Julius Constantius Flavia Julia Constantia
Names Marcus Flavius Valerius Constantius[a] Regnal name Imperator Caesar Marcus Flavius Constantius Augustus
Dynasty	Constantinian
Mother	Claudia
Religion	Ancient Roman religion

Of humble origin, Constantius had a distinguished military career and rose to the top ranks of the army. Around 289, he set asideHelena, Constantine's mother, to marry a daughter of EmperorMaximian, and in 293 was added to the imperial college by Maximian's colleague Diocletian. Assigned to ruleGaul, Constantius defeated the usurperCarausius there and his successorAllectus inBritain, and campaigned extensively along theRhine frontier, defeating theAlamanni andFranks. When theDiocletianic Persecution was announced in 303, Constantius ordered the demolition of churches but did not actively hunt down Christians in his domain.^[8] Upon becoming senior emperor in May 305, Constantius launched a successful punitive campaign against thePicts beyond theAntonine Wall.^[9] He died suddenly atEboracum (York) in July the following year.

After Constantius's death, the army, perhaps at his own instigation, immediately acclaimed his sonConstantine as emperor. This act contributed to the collapse of the Diocletianic tetrarchy, sparking a series of civil wars which only ended when Constantine finally united the whole Roman Empire under his rule in 324. According to theOxford Classical Dictionary, "Constantinian propaganda bedevils assessment of Constantius, yet he appears to have been an able general and a generous ruler".^[10] His descendants, theConstantinian dynasty, ruled the Empire until the death of his grandsonJulian in 363.

Constantius's birthday was 31 March; the year is unknown, but his career and the age of his eldest son imply a date no later than c. 250.^[2] Constantius was ofThracian origin, as his grandson, emperorJulian, explicitly wrote that their family came from "theMysians on the very banks of the Danube" and referred to them asThracians.^[11] He was born inNaissus, then inMoesia Superior,^[3] aRoman province on the south bank of theMiddle Danube later known asDacia Ripensis^[12] and was considered to be hailing from the region ofIllyricum.^[13][14] According to the unreliableHistoria Augusta he was the son of Eutropius, anobleman from the province ofMoesia Superior, andClaudia, a niece of the emperorsClaudius Gothicus andQuintillus.^[15] The same source also gives Claudius the nomina "FlaviusValerius" to strengthen his connection to Constantius.^[16] Modern historians suspect this maternal connection to be a genealogicalfabrication created by his sonConstantine I,^[17] and that his family was of humble origins.^[4][3][b] Constantine probably sought to dissociate his father's background from the memory of Maximian.^[18]

Constantius was a member of theProtectores Augusti Nostri under the emperorAurelian and fought in the east against the secessionistPalmyrene Empire.^[19] While the claim that he had been made adux under the emperorProbus is probably a fabrication,^[20][21] he certainly attained the rank oftribunus within the army, and during the reign ofCarus he was raised to the position ofpraeses, or governor, of the province ofDalmatia.^[22] It has been conjectured that he switched allegiances to support the claims of the future emperorDiocletian just before Diocletian defeatedCarinus, the son of Carus, at theBattle of the Margus in July 285.^[23]

In 286, Diocletian elevated a military colleague,Maximian, to the throne as co-emperor of the western provinces,^[24] while Diocletian took over the eastern provinces, beginning the process that would eventually see the division of theRoman Empire into two halves, aWestern and anEastern portion. By 288, his period as governor now over, Constantius had been madepraetorian prefect in the west under Maximian.^[25] Throughout 287 and into 288, Constantius, under the command of Maximian, was involved in a war against theAlamanni, carrying out attacks on the territory of thebarbarian tribes across theRhine andDanube rivers.^[24] To consolidate the ties between himself and Emperor Maximian, Constantius married the emperor's daughter,Theodora.^[19]

By 293,Diocletian, conscious of the ambitions of his co-emperor for his new son-in-law, allowed Maximian to promote Constantius in a new power sharing arrangement known as theTetrarchy. The eastern and western provinces would each be ruled by anaugustus, supported by acaesar. Bothcaesares had the right of succession once the rulingaugustus died.^[26]

AtMediolanum (Milan) on 1 March 293, Constantius was formally appointed as Maximian'scaesar.^[27] He adopted Diocletian'snomen (family name) "Valerius", and, being equated with Maximian, also took on "Herculius".^[28] His given command consisted ofGaul,Britannia and possiblyHispania.Diocletian, the easternaugustus, in order to keep the balance of power in theimperium,^[26] elevatedGalerius as hiscaesar, possibly on 21 May 293 atPhilippopolis (Plovdiv).^[19] Constantius was the more senior of the twocaesares, and on official documents he always took precedence, being mentioned before Galerius.^[28] Constantius's capital was to be located atAugusta Treverorum (Trier).^[29]

Constantius's first task on becomingcaesar was to deal with theRoman usurperCarausius who had declared himself emperor in Britannia and northern Gaul in 286.^[19] In late 293, Constantius defeated the forces of Carausius in Gaul, capturing Bononia (Boulogne-sur-Mer).^[30] Carausius was then assassinated by hisrationalis (finance officer)Allectus, who assumed command of the British provinces until his death in 296.^[31]

Constantius spent the next two years neutralising the threat of theFranks who were the allies of Allectus,^[32] as northern Gaul remained under the control of the British usurper until at least 295.^[33] He also battled against theAlamanni, achieving some victories at the mouth of theRhine in 295.^[34] Administrative concerns meant he made at least one trip to Italy during this time as well.^[32] Only when he felt ready (and only when Maximian finally came to relieve him at the Rhine frontier)^[35] did he assemble two invasion fleets with the intent of crossing theEnglish Channel. The first was entrusted toJulius Asclepiodotus, Constantius's long-servingPraetorian prefect, who sailed from the mouth of theSeine, while the other, under the command of Constantius himself, was launched from his base at Bononia.^[36] The fleet under Asclepiodotus landed near theIsle of Wight, and his army encountered the forces of Allectus, resulting in the defeat and death of the usurper.^[37] Constantius in the meantime occupiedLondinium (London),^[38] saving the city from an attack byFrankish mercenaries who were now roaming the province without a paymaster. Constantius massacred all of them.^[35]

Constantius remained in Britannia for a few months, replaced most of Allectus's officers, and the British provinces were probably at this time subdivided along the lines of Diocletian's other administrative reforms of the Empire.^[40] The result was the division ofBritannia Superior intoMaxima Caesariensis andBritannia Prima, whileFlavia Caesariensis andBritannia Secunda were carved out ofBritannia Inferior. He also restoredHadrian's Wall and its forts.^[41]

Later in 298, Constantius fought in theBattle of Lingones (Langres) against theAlemanni. He was shut up in the city, but was relieved by his army after six hours and defeated the enemy.^[42] Hedefeated them again at Vindonissa^[43] thereby strengthening the defences of theRhine frontier. In 300, he fought against theFranks on the Rhine frontier,^[44] and as part of his overall strategy to buttress the frontier, Constantius settled the Franks in the deserted parts ofGaul to repopulate the devastated areas.^[45] Nevertheless, over the next three years the Rhine frontier continued to occupy Constantius's attention.^[44]

From 303 – the beginning of theDiocletianic Persecution – Constantius began to enforce the imperial edicts dealing with thepersecution of Christians, which ordered the destruction ofchurches.^[18] The campaign was avidly pursued byGalerius, who noticed that Constantius was well-disposed towards theChristians, and who saw it as a method of advancing his career prospects with the aging Diocletian.^[46] Of the four Tetrarchs, Constantius made the least effort to implement the decrees in the western provinces that were under his direct authority,^[47] limiting himself to knocking down a handful of churches.^[25]Eusebius denied that Constantius destroyed Christian buildings, butLactantius records that he did.^[18]

Between 303 and 305, Galerius began maneuvering to ensure that he would be in a position to take power from Constantius after the death of Diocletian.^[48] In 304, Maximian met with Galerius, probably to discuss the succession issue and Constantius either was not invited or could not make it due to the situation on the Rhine.^[44] Although prior to 303 there appeared to be tacit agreement among the Tetrarchs that Constantius's sonConstantine and Maximian's sonMaxentius were to be promoted to the rank ofcaesar once Diocletian and Maximian had resigned the purple,^[49] by the end of 304 Galerius had convinced Diocletian (who in turn convinced Maximian) to appoint Galerius's nomineesSeverus andMaximinus ascaesares.^[44]

Diocletian and Maximian stepped down as co-emperors on 1 May 305, possibly due to Diocletian's poor health.^[25] Before the assembled armies at Mediolanum, Maximian removed his purple cloak and handed it to Severus, the newcaesar, and proclaimed Constantius asaugustus. The same scene played out atNicomedia (İzmit) under the authority of Diocletian.^[50] Constantius, notionally the senior emperor, ruled the western provinces, while Galerius took the eastern provinces. Constantine, disappointed in his hopes to become acaesar, fled the court of Galerius after Constantius had asked Galerius to release his son as Constantius was ill.^[51] Constantine joined his father's court at the coast of Gaul, just as he was preparing to campaign in Britain.^[52]

In 305, Constantius crossed over into Britain, travelled to the far north of the island and launched a military expedition against thePicts, claiming a victory against them and the titleBritannicus Maximus II by 7 January 306.^[53] After retiring toEboracum (York) for the winter, Constantius had planned to continue the campaign, but on 25 July 306 he died.^[54] As he was dying, Constantius recommended his son to the army as his successor;^[55] consequently,Constantine was declared emperor by the legions at York.^[56]

Constantius was either married to, or was in concubinage with,Helena, who was probably fromNicomedia in Asia Minor.^[57] They had one son, the future emperorConstantine the Great.

In 289, political developments forced him to divorceHelena. He marriedTheodora,Maximian's daughter. They had six children:^[20]

• Flavius Dalmatius
• Julius Constantius
• Flavius Hannibalianus
• Flavia Julia Constantia
• Anastasia, married toBassianus
• Eutropia

The name of Anastasia (Koinē Greek:Ἀναστασία,romanized: Anastasía,lit. 'resurrection') may indicate a sympathy with Christian or Jewish culture.^[3]

As the father of Constantine, a number of Christian legends have grown up around Constantius. Eusebius'sLife of Constantine claims that Constantius was himself a Christian, although he pretended to be a pagan, and while Caesar under Diocletian, took no part in the Emperor's persecutions.^[58] It was claimed that his first wife,Helena, found theTrue Cross.^{[citation needed]}

Constantius's activities in Britain were remembered inmedieval Welsh legend, which frequently confused his family with that ofMagnus Maximus, who also was said to have wed aSaint Elen and sired a son named Constantine while in Britain.Henry of Huntingdon'sHistory of the English identified Constantius's wife Helen as British^[59] andGeoffrey of Monmouth repeated the claim in his 1136History of the Kings of Britain. Geoffrey related that Constantius was sent to Britain by theSenate afterAsclepiodotus (here a British king) was overthrown byCoel ofColchester. Coel submitted to Constantius and agreed to pay tribute to Rome, but died only eight days later. Constantius married his daughter Helena and becameking of Britain. He and Helena had a son, Constantine, who succeeded to the throne of Britain when his father died atYork eleven years later.^[60] These accounts have no historical validity: Constantius had divorced Helena before he went to Britain.^[61]

Similarly, theHistory of the Britons traditionally ascribed toNennius^[62] claims the inscribed tomb of "Constantius the Emperor" was still present in the 9th century in the Roman fort ofSegontium (near present-dayCaernarfon, inNorth Wales).^[63] David Nash Ford credited the monument to Constantine, the supposed son of Magnus Maximus and Elen, who was said to have ruled over the area prior to theIrish invasions.^[64]