One of the most tragic page of the history of Roman Empire was the Battle of Edessa. Let’s start with introduction of main characters of the event. So..
Roman Emperor Valerian was member of a noble Roman family and assumed his post during the Crisis of the Third Century. Civil wars were common in Roman Empire in that time and the soldiers proclaimed Valerian emperor after emperor Trebonianus Gallus was killed by his own troops. During his reign he followed the policy of persecution of Christians and even ordered the execution of bishop of Rome Pope Sixtus II.
Shapur I was King of Kings of Iran and Aniran, or simply the King of Persia. Since his raise to power in 241 he began to centralize power in the Empire. Initially he shared the throne with his father, but after death of the latter be became the sole ruler of the Sasanian Empire. Shapur liked reliefs and inscription on rocks and left many of them. He called himself worshiper of Mazda. Mazda here is not a Japanese car, but the sole God of Zoroastrianism.
Shapur I also was a quite bellicose and launched some attacks on Roman Empire. Some of them were successful. Thus he managed to conquest Antioch in 253. Valerian began to prepare for the reply, and combine Roman army including praetorians. In 206 he invaded Persia and met the forces of Shapur I near the city of Edessa. After initial troubles Valerian tried to negotiate with Shapur, but it seems that during Shapur negotiations the Roman Emperor was seized while Roman army was forced to surrender. The most Lactantius pessimistic sources said about unpleasant consequences. Persian Emperor kept Valerian in cruel conditions and was humiliated there. Shapur used him as a step to climb into his horse. It also said that Valerian was kept in a cage. After Valerian’s death Shapur ordered to skin him and stuffed with manure.
After the battle Shapur tried to capture Cilicia but was defeated by Roman army. One of generals who participated in this operation proclaimed his sons as Emperors.