Excerpts from Books and Wikipedia
"The Romans were down on their luck, and in 260, Roman Emperor Valerian was defeated by Persian King Shapur I at Edessa (modern-day Urfa, Turkey). Valerian was taken prisoner and subjected to various humiliations, including, reputedly, being used as a human footstool. He died in captivity. . . . After its conquest by Alexander the Great in the fourth century B.C.E., Persia was ruled by foreign dynasties until 224-226, when the Sasanian dynasty came to power. Vigorous and ambitious, the Sasanians aspired to regain for Persia the superpower status it had enjoyed under the Achaemenid dynasty (559-330 B.C.E.). . . . In the aftermath of the battle, Roman fortunes sank to a new low. Britain and Gaul declared independence, and the 'Thirty Tyrants' fought for power in the east. In 261, Shapur was defeated by Odaenathus, the Romanized Arab ruler of Palmyra. The Romans regained control of the area in 274 when they defeated Odaenathus's widow, Zenobia." [1001 Days]