Nepotianus (died 30 June 350 AD), sometimes known in English as Nepotian,^[1] was a member of the Constantinian dynasty who reigned as a short-lived usurper of the Roman Empire. He ruled the city of Rome for twenty-eight days, before being killed by his rival usurper Magnentius' general Marcellinus.^[1]

Nepotianus was the son of Eutropia, half-sister of Emperor Constantine I,^[4] and of Virius Nepotianus. On his mother's side, he was the grandson of Emperor Constantius Chlorus and Flavia Maximiana Theodora.^[5]

After the revolt of Magnentius, Nepotianus proclaimed himself emperor and entered Rome with a band of gladiators^[4] on 3 June 350.^[1] After attempting to resist Nepotianus with an undisciplined force of Roman citizens, the defeated praefectus urbi Titianus (or Anicius, or Anicetus), a supporter of Magnentius, fled the city.

Magnentius quickly dealt with this revolt^[4] by sending his trusted magister officiorum Marcellinus to Rome. According to Eutropius, Nepotianus was killed in the resulting struggle (on 30 June), his head put on a lance and borne around the city.^[4] In the following days, his mother Eutropia was also killed alongside the supporters of Nepotianus.^[5]

• List of Roman emperors
• List of Roman usurpers