Kings of Iran ad 224–651. The dynasty, very often labelled heirs to the Achaemenids, actually owed much more to the Parthians (see parthia). Their empire at its greatest extent stretched from Syria to India and from Caucasian Iberia to the Persian Gulf. The Sasanids constantly sought to alter the military status quo in the Mesopotamian, Armenian, and Syrian areas; and the forts of the Euphrates limes were strengthened against attacks from them. Major campaigns were undertaken against them by various Roman emperors. Valerian was defeated and captured by Sapor I, Diocletian and Galerius defeated Narsēs in 297, Jovian had to make large concessions to Sapor II after the death of Julian in Mesopotamia (363).
Though Zoroastrianism (see zoroaster) was the most important cult in Sasanid Iran, and although most kings tried to present themselves as devout Mazda‐worshippers and a priestly hierarchy developed in the course of time, religious minorities like the Christians, the Manichaeans, and the Jews were allowed to practise their faith.