Constantius Chlorus

Flavius Valerius Constantius "Chlorus" ( – 25 July 306), also called Constantius I, was a Roman emperor as one of the four original members of the "Tetrarchy" established by Diocletian in 293. He was a junior-ranking emperor, or "Caesar", from 293 to 305, and senior emperor, "Augustus", from 305 to 306. Constantius was also the father of Constantine the Great, the first Christian emperor of Rome. The nickname Chlorus () was first popularized by Byzantine-era historians and was not used during the emperor's lifetime.
Of Illyrian and probably humble origin, Constantius had a distinguished military career and rose to the top ranks of the army. Around 289 he set aside Helena, Constantine's mother, to marry a daughter of Emperor Maximian, and in 293 was added to the imperial college by Maximian's colleague, Diocletian. Assigned to rule Gaul, Constantius defeated the usurper Carausius there and his successor Allectus in Britain, and campaigned extensively along the Rhine frontier, defeating the Alamanni and Franks. When the Diocletianic Persecution was announced in 303, Constantius ordered the demolition of churches but did not actively hunt down Christians in his domain. Upon becoming senior emperor in May 305, Constantius launched a successful punitive campaign against the Picts beyond the Antonine Wall. He died suddenly at Eboracum (York) in July the following year.
After Constantius's death, the army, perhaps at his own instigation, immediately acclaimed his son Constantine 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 the "Oxford Classical Dictionary", "Constantinian propaganda bedevils assessment of Constantius, yet he appears to have been an able general and a generous ruler". His descendants, the Constantinian dynasty, ruled the Empire until the death of his grandson Julian in 363.
Life.
Early career.
Constantius's birthday was 31 March; the year is unknown, but his career and the age of his eldest son a imply date no later than c. 250. Constantius was born in Dacia Ripensis, a Roman province on the south bank of the Middle Danube – the empire's frontier – with its capital at Ratiaria (modern Archar). He was the son of Eutropius, whom the "Historia Augusta" claimed to be a nobleman from northern Dardania, in the province of Moesia Superior, and Claudia, a niece of the emperors Claudius Gothicus and Quintillus. Modern historians suspect this maternal connection to be a genealogical fabrication created by his son Constantine I, and that his family was of humble origins. Constantine probably sought to dissociate his father's background from the memory of Maximian. The claim that Constantius was descended from Claudius Gothicus is attested only after 310 and does not appear to have been made while Constantius was alive. 
Constantius was a member of the "Protectores Augusti Nostri" under the emperor Aurelian and fought in the east against the secessionist Palmyrene Empire. While the claim that he had been made a "dux" under the emperor Probus is probably a fabrication, he certainly attained the rank of "tribunus" within the army, and during the reign of Carus he was raised to the position of "praeses", or governor, of the province of Dalmatia. It has been conjectured that he switched allegiances to support the claims of the future emperor Diocletian just before Diocletian defeated Carinus, the son of Carus, at the Battle of the Margus in July 285.
In 286, Diocletian elevated a military colleague, Maximian, to the throne as co-emperor of the western provinces, while Diocletian took over the eastern provinces, beginning the process that would eventually see the division of the Roman Empire into two halves, a Western and an Eastern portion. By 288, his period as governor now over, Constantius had been made Praetorian Prefect in the west under Maximian. Throughout 287 and into 288, Constantius, under the command of Maximian, was involved in a war against the Alamanni, carrying out attacks on the territory of the barbarian tribes across the Rhine and Danube rivers. To consolidate the ties between himself and Emperor Maximian, Constantius divorced his concubine Helena and married the emperor's daughter, Theodora.
Elevation as Caesar.
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 the Tetrarchy. The eastern and western provinces would each be ruled by an Augustus, supported by a Caesar. Both Caesars had the right of succession once the ruling Augustus died.
At Mediolanum (Milan) on March 1, 293, Constantius was formally appointed as Maximian's Caesar. He adopted the name "Flavius Valerius Constantius", and, being equated with Maximian, also took on "Herculius". His given command consisted of Gaul, Britannia and possibly Hispania. Diocletian, the eastern Augustus, in order to keep the balance of power in the "imperium", elevated Galerius as his Caesar, possibly on May 21, 293 at Philippopolis (Plovdiv). Constantius was the more senior of the two Caesars, and on official documents he always took precedence, being mentioned before Galerius. Constantius' capital was to be located at Augusta Treverorum (Trier).
Constantius' first task on becoming Caesar was to deal with the Roman usurper Carausius who had declared himself emperor in Britannia and northern Gaul in 286. In late 293, Constantius defeated the forces of Carausius in Gaul, capturing Bononia (Boulogne-sur-Mer). This precipitated the assassination of Carausius by his "rationalis" (finance officer) Allectus, who assumed command of the British provinces until his death in 296.
Constantius spent the next two years neutralising the threat of the Franks who were the allies of Allectus, as northern Gaul remained under the control of the British usurper until at least 295. He also battled against the Alamanni, achieving some victories at the mouth of the Rhine in 295. Administrative concerns meant he made at least one trip to Italy during this time as well. Only when he felt ready (and only when Maximian finally came to relieve him at the Rhine frontier) did he assemble two invasion fleets with the intent of crossing the English Channel. The first was entrusted to Julius Asclepiodotus, Constantius' long-serving Praetorian prefect, who sailed from the mouth of the Seine, while the other, under the command of Constantius himself, was launched from his base at Bononia. The fleet under Asclepiodotus landed near the Isle of Wight, and his army encountered the forces of Allectus, resulting in the defeat and death of the usurper. Constantius in the meantime occupied Londinium (London), saving the city from an attack by Frankish mercenaries who were now roaming the province without a paymaster. Constantius massacred all of them.
Constantius remained in Britannia for a few months, replaced most of Allectus' officers, and the British provinces were probably at this time subdivided along the lines of Diocletian's other administrative reforms of the Empire. The result was the division of Britannia Superior into Maxima Caesariensis and Britannia Prima, while Flavia Caesariensis and Britannia Secunda were carved out of Britannia Inferior. He also restored Hadrian's Wall and its forts.
Later in 298, Constantius fought in the Battle of Lingones (Langres) against the Alemanni. He was shut up in the city, but was relieved by his army after six hours and defeated the enemy. He defeated them again at Vindonissa (Windisch), thereby strengthening the defences of the Rhine frontier. In 300, he fought against the Franks on the Rhine frontier, and as part of his overall strategy to buttress the frontier, Constantius settled the Franks in the deserted parts of Gaul to repopulate the devastated areas. Nevertheless, over the next three years the Rhine frontier continued to occupy Constantius' attention.
From 303 – the beginning of the Diocletianic Persecution – Constantius began to enforce the imperial edicts dealing with the persecution of Christians, which ordered the destruction of churches. The campaign was avidly pursued by Galerius, who noticed that Constantius was well-disposed towards the Christians, and who saw it as a method of advancing his career prospects with the aging Diocletian. Of the four Tetrarchs, Constantius made the least effort to implement the decrees in the western provinces that were under his direct authority, limiting himself to knocking down a handful of churches. Eusebius denied that Constantius destroyed Christian buildings, but Lactantius records that he did.
Accession as Augustus and death.
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. 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. Although prior to 303 there appeared to be tacit agreement among the Tetrarchs that Constantius's son Constantine and Maximian's son Maxentius were to be promoted to the rank of Caesar once Diocletian and Maximian had resigned the purple, by the end of 304 Galerius had convinced Diocletian (who in turn convinced Maximian) to appoint Galerius's nominees Severus and Maximinus Daia as Caesars.
Diocletian and Maximian stepped down as co-emperors on May 1, 305, possibly due to Diocletian's poor health. Before the assembled armies at Mediolanum, Maximian removed his purple cloak and handed it to Severus, the new "Caesar", and proclaimed Constantius as "Augustus". The same scene played out at Nicomedia (İzmit) under the authority of Diocletian. Constantius, notionally the senior emperor, ruled the western provinces, while Galerius took the eastern provinces. Constantine, disappointed in his hopes to become a Caesar, fled the court of Galerius after Constantius had asked Galerius to release his son as Constantius was ill. Constantine joined his father's court at the coast of Gaul, just as he was preparing to campaign in Britain.
In 305 Constantius crossed over into Britain, travelled to the far north of the island and launched a military expedition against the Picts, claiming a victory against them and the title "Britannicus Maximus II" by 7 January 306. After retiring to Eboracum (York) for the winter, Constantius had planned to continue the campaign, but on 25 July 306, he died. As he was dying, Constantius recommended his son to the army as his successor; consequently Constantine was declared emperor by the legions at York.
Family.
Constantius was either married to, or was in concubinage with, Helena, who was probably from Nicomedia in Asia Minor. They had one son: Constantine.
In 289 political developments forced him to divorce Helena. He married Theodora, Maximian's daughter. They had six children:
The name of Anastasia () may indicate a sympathy with Christian or Jewish culture. 
Legend.
Christian legends.
As the father of Constantine, a number of Christian legends have grown up around Constantius. Eusebius's "Life 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. It was claimed that his first wife, Helena, found the True Cross.
British legends.
Constantius's activities in Britain were remembered in medieval Welsh legend, which frequently confused his family with that of Magnus Maximus, who also was said to have wed a Saint Elen and sired a son named Constantine while in Britain. Henry of Huntingdon's "History of the English" identified "Constantius's" wife Helen as British and Geoffrey of Monmouth repeated the claim in his 1136 "History of the Kings of Britain". Geoffrey related that Constantius was sent to Britain by the Senate after Asclepiodotus (here a British king) was overthrown by Coel of Colchester. Coel submitted to Constantius and agreed to pay tribute to Rome, but died only eight days later. Constantius married his daughter Helena and became king of Britain. He and Helena had a son, Constantine, who succeeded to the throne of Britain when his father died at York eleven years later. These accounts have no historical validity: Constantius had divorced Helena before he went to Britain.
Similarly, the "History of the Britons" traditionally ascribed to Nennius mentions the inscribed tomb of "Constantius the Emperor" was still present in the 9th century in Segontium (near present-day Caernarfon, Wales). 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 the Irish invasions.