The rise of the Sasanian Empire ignited a ferocious struggle for dominance in the Near East, challenging Rome’s eastern frontier like never before. Initiated by Ardashir I and intensified by Shapur I—who famously captured Emperor Valerian—the conflict saw control of Mesopotamia swing violently between the two powers. Although Rome secured a decisive victory under Galerius in 298 AD, Shapur II later renewed hostilities, engaging in a grueling war of attrition over key fortress cities like Nisibis and Amida. The era culminated in Emperor Julian’s ill-fated 363 AD campaign, where his death and the subsequent peace treaty forced Rome to cede significant territory, reshaping the balance of power in the region.
https://en.wikipedia.org/wiki/Roman%E2%80%93Persian_wars#Roman%E2%80%93Sasanian_wars