"Flavius Valerius Constantius "Chlorus" (c. 250 – 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 father of Constantine the Great, the first Christian emperor of Rome. The nickname Chlorus (Greek: Χλωρός, lit. "the Green") was first popularized by Byzantine-era historians and 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." - (en.wikipedia.org 11.08.2021)
