Excerpts from Books and Wikipedia
"In about 224 CE, the last Parthian king was overthrown by Ardashir, a leading member of the Sassanian dynasty from Fars, Persia. He founded a dynasty that ruled Persia for over 400 years. His son, Shapur I (240-272) expanded the empire's borders to include modern Iran, Iraq, parts of Afghanistan, Pakistan, and Central Asia. Sassanian Persia became a major threat to Roman interests in Asia, and the two powers were frequently in conflict." [DK Timelines, p. 91] "With the conclusion of the Roman-Persian wars, the war-exhausted Persians lost the Battle of al-Qâdisiyah (632) in Hilla, (present day Iraq) to the invading forces of Islam." [Wikipedia] "Both Ardashir I and Shapur I were Zoroastrians, adherents of a mystical religion first preached by the prophet Zoroaster (or Zarathustra) back in the days of Darius I. . . . By the time of Shapur I it taught that the universe was divided into two equally powerful opposing forces of good and evil. . . . Ardashir himself had proclaimed Zoroastrianism the state religion of his new empire, which drew every one of his subjects together into a holy community with a single purpose." [Bauer: Ancient World, p. 765]