Flavius Julius Constans (c. 323 – 350), also called Constans I, was Roman emperor from 337 to 350. He held the imperial rank of Caesar from 333, and was the youngest son of Constantine the Great.
 
In January 350, Magnentius (r. 350–353) the commander of the Jovians and Herculians, a corps in the Roman army, was acclaimed augustus at Augustodunum (Autun) with the support of Marcellinus, the comes rei privatae. Magnentius overthrew and killed Constans. Surviving sources, possibly influenced by the propaganda of Magnentius's faction, accused Constans of misrule and of homosexuality.