| Constantius III | |
|---|---|
 Consular diptych of Constantius III | |
| Roman emperor of the West | |
| Reign | 8 February – 2 September 421 (with Honorius) |
| Born | Constantius Naissus, Moesia |
| Died | 2 September 421 Ravenna, Italia |
| Spouse | Galla Placidia |
| Issue | |
| Dynasty | Theodosian |
Constantius III (died 2 September 421) was briefly Western Roman emperor in 421, having earned the throne through his capability as a general under Honorius. By 411 he had achieved the rank of magister militum, and in the same year he suppressed the revolt of the usurper Constantine III. Constantius went on to lead campaigns against various barbarian groups in Hispania and Gaul, recovering much of both for the Western Roman Empire. He 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. Constantius reigned for seven months before dying on 2 September 421.