Shapur I becomes co-emperor of the Sasanian Empire with his father Ardashir I.

Shapur I was the second Sasanian King of Kings of Iran. The precise dating of his reign is disputed, but it is generally agreed that he ruled from 240 to 270, with his father Ardashir I as co-regent until the death of the latter in 242. During his co-regency, he helped his father with the conquest and destruction of the city of Hatra, whose fall was facilitated, according to the Islamic myth, by the actions of his future wife al-Nadirah. Shapur also consolidated and expanded the empire of Ardashir I, waged war against the Roman Empire, and seized its cities of Nisibis and Carrhae while he was advancing as far as Roman Syria. Although he was defeated at the Battle of Resaena in 243 by Roman emperor Gordian III, the following year he was able to win the Battle of Misiche and force the new Roman emperor Philip the Arab to sign a favorable peace treaty that was regarded by the Romans as "a most shameful treaty".