The Sasanian Empire began in 226 C.E., when Ardashir, a Persian satrap, revolted against his Parthian overlords. Occupying the territories now divided among Iran and Iraq, and for brief periods Syria and Armenia, the empire engaged in intermittent warfare with Rome and Byzantium and was beset by internal strife as kings sought to impose Zoroastrianism upon the population and fought each other for power. In 640 C.E. the empire succumbed to the Arab...