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 from 293 to 305, and senior emperor from 305 to 306.Constantius was also father of Constantine the Great, the first Christian emperor of Rome.

Constantius was born in 317 at Sirmium, Pannonia.He was the third son of Constantine the Great, and second by his second wife Fausta, the daughter of Maximian.Constantius was made caesar by his father on 8 November 324. In 336, religious unrest in Armenia and tense relations between Constantine and king Shapur II caused war to break out between Rome and Sassanid Persia.

Flavius Valerius Constantius (nicht zeitgenössischer Beiname Chlorus „der Grüne, Blasse“; kurz Constantius I.; * um 250; † 306 in Eboracum, heute York) war ein Kaiser der römischen Tetrarchie.Zunächst von 293 bis 305 untergeordneter Caesar, war er in den Jahren 305/306 Augustus im westlichen Reichsteil. Als Kaiser sorgte er vor allem für die Beendigung des …