Constantius I (Latin: Marcus Flavius Valerius Constantius Herculius Augustus; 31 March c.?250 – 25 July 306), commonly known as Constantius Chlorus (Greek: ???st??t??? ??????, Konstantios Khlorós, literally "Constantius the Pale"), was a Caesar from 293 to 305 and a Roman Emperor from 305 to 306.
He was the father of Constantine the Great and founder of the Constantinian dynasty.
As Caesar, a junior emperor, he defeated the usurper Allectus in Britain and campaigned extensively along the Rhine frontier, defeating the Alamanni and Franks.
Upon becoming Augustus in 305, Constantius launched a successful punitive campaign against the Picts beyond the Antonine Wall.
However, Constantius died suddenly in Eboracum (York) the following year.
His death sparked the collapse of the tetrarchic system of government inaugurated by the Emperor Diocletian.