Founding of the Sasanian Empire

The Sasanian Empire was founded in 224 CE when Ardashir I, a regional ruler from Persis in what is now southern Iran, defeated and killed the last Parthian king, Artabanus IV, at the Battle of Hormozdgan, ending nearly four centuries of Parthian Arsacid rule over Persia. Ardashir, who traced his lineage to the Sasan family and invoked the earlier Achaemenid tradition, was crowned King of Kings and established a new, more centralized state that made Zoroastrianism its official state religion under an organized priesthood. His son and successor Shapur I expanded the empire dramatically, defeating three Roman emperors in the third century, including capturing the emperor Valerian in 260 CE, and the Sasanian state went on to rule Persia and Mesopotamia for more than four centuries, becoming Rome's, and later Byzantium's, principal eastern rival until the Muslim conquest of Persia in the seventh century.