Numerian (Latin: Marcus Aurelius Numerius Numerianus;[2] died November 284) was Roman emperor from 283 to 284 with his older brother Carinus.

[9] In 283, Carus left Carinus in charge of the West and moved with Numerian and his praetorian prefect Arrius Aper to the East to wage war against the Sassanid Empire.

[10][11] According to Zonaras, Eutropius, and Festus, Carus won a major victory against the Persians, taking Seleucia and the Sassanid capital of Ctesiphon (near modern Al-Mada'in, Iraq), cities on opposite banks of the Tigris.

[22] Aper officially broke the news of Numerian's death in Nicomedia (İzmit) in November 284,[23] and the discovery, which the prefect attempted to conceal, as due to the forwardness of the soldiery, who forced open the Imperial tent to investigate for themselves the situation of their invisible monarch.

[21] Numerian's generals and tribunes called a council for the succession, which met at Chalcedon across the Bosphorus, where they chose as emperor Diocletian, commander of the cavalry arm of the imperial bodyguard,[24] despite Aper's attempts to garner support.

Diocletian accepted the purple imperial vestments and raised his sword to the light of the sun, swearing an oath denying responsibility for Numerian's death.