Constantius I, as Caesar. (AD 293–305).
                        Bil follis.

                        ROMAN EMPIRE. Constantius I, as Caesar (AD 293–305). Bil
                        follis . Londinium, from ca. AD 300. FL VAL
                        CONSTANTIVS NOB C, laureate, cuirassed bust of
                        Constantius right / As preceding, but no mint marks. RIC
                        20.  
                        

Constantius I. Flavius Valerius, surnamed Chlorus (ὁ Χλωρός, "the pale"), Roman emperor, A.D. 305, 306, father of Constantine the Great, son of Eutropius, of a noble Dardanian family, by Claudia, daughter of Crispus, brother of the emperors Claudius II. and Quintilius. Born c. a.d. 250. Distinguished by ability, valour, and virtue, Constantius became governor of Dalmatia under the emperor Carus, who was prevented by death from making him his successor. Diocletian (emperor, a.d. 284–305), to lighten the cares of empire, associated Maximian with himself; and arranged that each emperor should appoint a co-regent Caesar. Constantius was thus adopted by Maximian, and Galerius by Diocletian, (Mar. 1, a.d. 292). Each being obliged to repudiate his wife and marry the daughter of his adopted father, Constantius separated from Helena, the daughter of an innkeeper, who was not his legal wife but was mother of Constantine the Great, and married Theodore, stepdaughter of Maximian, by whom he had six children. As his share of the empire, Constantius received the provinces Gaul, Spain, and Britain. In a.d. 296 he reunited Britain to the empire, after the rebellion of Carausius, and an independence of ten years. In a.d. 305, after the abdication of Diocletian and Maximian, Galerius and Constantius became Augusti, and ruled together. As the health of Constantius began to fail, he sent for his son Constantine, who was already exceedingly popular, and who was jealously kept by Galerius at his own court. Constantine escaped, and arrived at his father's camp at Gessoriacum (Boulogne-sur-Mer) before embarking on another expedition to Britain. In a.d. 306 Constantius died in the imperial palace at Eboracum (York). He is described as one of the most excellent characters among the later Romans. He took the keenest interest in the welfare of his people, and limited his personal expenses to the verge of affectation, declaring that "his most valued treasure was in the hearts of his people." The Gauls delighted to contrast his gentleness and moderation with the haughty sternness of Galerius. His internal administration was as honourable as his success in war. The Christians always praised his tolerance and impartiality. Theophanes calls him Χριστιανόφρων, a man of Christian principles. He had Christians at his court. Although a pagan, he disapproved of the persecution of Diocletian, and contented himself by closing a few churches and overthrowing some dilapidated buildings, respecting (as the author of the de Morte Persecutorum says) the true temple of God. Christianity spread in Gaul under his peaceful rule, and at the end of the 4th cent. that province had more than 20 bishops.

The Historia Augusta says Constantius was the son of Eutropius, a noble from northern Dardania in modern Serbia, and Claudia, a niece of the emperors Claudius II and Quintillus. Historians, however, suspect this maternal connection to be a genealogical fabrication created by his grandson Constantine II, thus connecting his family to two rather highly regarded predecessors. Under the emperor Carus, he was governor of Dalmatia, and Carus is said to have considered adopting him as his heir in place of his dissolute son, Carinus.

In 293 the emperor Diocletian created the Tetrarchy, dividing the Roman Empire into Western and Eastern portions. Each would be ruled by an Augustus, supported by a Caesar. Diocletian became Augustus of the Eastern empire, with Galerius as his Caesar. Constantius was appointed Caesar to the Western Augustus, Maximian, and married Theodora, Maximian's stepdaughter. They had six children. Constantius divorced his first wife (or concubine), Helena, by whom he already had a son, Constantine. Helena was probably from Nicomedia in Asia Minor. He was given command of Gaul, Britain and possibly Hispania.

On the reverse of this argenteus struck in Antioch under Constantius Chlorus, the tetrarchs are sacrificing to celebrate a victory against the Sarmatians.

In 293, Constantius defeated the forces of Carausius, who had declared himself emperor in Britain and northern Gaul in 286, near Bononia. Carausius was killed by his rationalis Allectus, who took command of Britain until 296, when Constantius sent Asclepiodotus, a prefect of the Praetorian Guard, to invade the island. Allectus was defeated and killed, and Roman rule in Britain restored.

Also in 296, Constantius fought a battle against the Alamanni at the city of Lingonae (Langes) in Gaul. 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, Switzerland), thereby strengthening the defenses of the Rhine frontier.

Diocletian and Maximian stepped down as co-emperors in 305, due to Diocletian's poor health, and the Caesars, Constantius and Galerius, became co-emperors. Constantius ruled the western empire, Galerius the eastern. Severus and Maximinus were appointed Caesars. Constantine, who had hoped to be a Caesar, joined his father's campaigns in Gaul and Britain. Constantius died in Britain, at York, in 306, and Constantine was declared emperor by the army