The Historia Augusta says Constantius was the son of Eutropius, a noble from northern Dardania in modern Kosovo, and Claudia, a niece of the emperors Claudius II and Quintillus. Under the emperor Carus, he was governor of Dalmatia. 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. 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.

Main Roman Coin Book and Other References:

RIC = Mattingly, Harold    The Roman Imperial Coinage
BMC = Coins of the Roman Empire in the British Museum
RSC = Seaby, H A    Roman Silver Coinage
RCV = Sear, David R    Roman Coins and Their Values
Cr = Crawford, Michael    The Roman Republican Coinage
SB = Sear, David R    Byzantine Coins and Their Values
S = Coins of England and the United Kingdom
WW = Wildwinds.com (reference & attribution site)