Shapur I, son of Ardashir I reigned over the Sassanian Empire from 241 to 272. Towards the end of his rule, Ardashir had revived the war against the Roman Empire. Shapur continued it, conquering the Mesopotamian fortresses of Carrhae and Nisibis and entering Syria, although his forces were there rejected by the father in law of the young Emperor Gordian III, Timesitheus, and finally defeated in the Battle of Rasaena in 243, forcing him to leave Mesopotamia.
Shortly after, Timesitheus died and Gordian was murdered by Philip the Arab, who signed a truce with Persians in 244. Shapur reignited the war shortly after, taking advantage of the Goths´ invasion of the Empire and the continuous succession of emperors that followed the death of Decian (251).
Shapur conquered Armenia, invaded Syria and sacked Antioch. Valerian tried to march against him, but was taken as a prisoner when trying to start negotiations. Shapur entered Asia Minor although was finally rejected by Allistus. Septimius Ordenatus, king of Palmyra, defeated the Persian army, reconquered Carrhae and Nisibis and even kidnapped the royal harem.
The Sassanian Emperor could not recover and even lost Armenia again. According to Persian sources, he managed to recover Hatra, in the Mesopotamia desert, and above all, he attained glory for keeping Valerian, the Roman Emperor, as hostage.
In the Valley of Istair, near Persepolis, under the Achemenid tombs in Nakshi Rustam, Shapur is represented riding a horse, wearing a royal armour and crown, with Valerian on his knees begging for mercy. The same scene is represented and can still be seen in the ruins of several cities of today´s Iran.
Shapur on his coins and inscriptions calls himself a “worshiper of Mazda” the god of Zoroastrianism, king of Arian and non-Arian kings, grandson of the king-god Papak, which made him king of all the world, although his territories were even smaller that his father´s, Ardashir I.