Constantius III (in Latin: Flavius Constantius) was Roman emperor of the West in 421, from 8 February until his death on 2 September. He earned his position as Emperor due to his capability as a general under Honorius, achieving the rank of magister militum by 411. That same year, he suppressed the revolt of Constantine III, a Roman general who had declared himself emperor. Constantius then went on to lead campaigns against various barbarian groups in Hispania and Gaul, recovering much of both for the Western Roman Empire. Constantius married Honorius's sister Galla Placidia in 417, a sign of his ascendant status, and was proclaimed co-emperor by Honorius on 8 February 421. He reigned for seven months before dying on 2 September 421.