The Sasanians, 224–636

Around 224 A.D., Ardashir I, a descendant of Sasan who gave his name to the new Sasanian dynasty, defeated the Parthians. The Sasanians saw themselves as the successors of the Achaemenid Persians. One of the most energetic and able Sasanian rulers was Shapur I (r. 241—72 A.D.). During his reign, the central government was strengthened, the coinage was reformed, and Zoroastrianism was made the state religion. The expansion of Sasanian power in the west brought conflict with Rome. In 260 A.D., Shapur took prisoner the emperor Valerian in a battle near Edessa. Thereafter the defense of Rome's eastern frontier was left to the ruler of Palmyra, a caravan city in Syria. By the end of Shapur I’s reign, the Sasanian empire stretched from the River Euphrates to the River Indus and included modern-day Armenia and Georgia. After a short period during which much territory was lost, Sasanian fortunes were restored during the long reign of Shapur II (r. 310—79 A.D.). He reestablished control over the Kushans in the east and campaigned in the desert against the Arabs. Conflict with Rome resulted once again in Sasanian control of northern Mesopotamia and Armenia. During the fifth century, tribal movements in Central Asia resulted in Hephthalite Huns creating an extensive empire centered on Afghanistan. After a disastrous campaign, the Sasanians were forced to pay tribute to their new eastern neighbors. Iran recovered her glory during the reign of Khosrow I (r. 531—79 A.D), who defeated the Hephthalites. However, in the years following Khosrow's death, there were internal revolts and wars with the Byzantine empire. This weakened Iran, and Arab forces, united under Islam, defeated the Sasanian armies in 642. The last Sasanian ruler, Yazdegerd III, died in 651.