The region now called Iran was occupied by the Medes and the Persians in the 1500s B.C., until the Persian king Cyrus the Great overthrew the Medes and became ruler of the Achaemenid (Persian) Empire, which reached from the Indus to the Nile at its zenith in 525 BC. Persia fell to Alexander in 331330 B.C. and a succession of other rulers: the Seleucids (312302 BC), the Greek-speaking Parthians (247 BCAD 226), the Sasanians (224c. 640), and the Arab Muslims (in 641). By the mid-800s Persia had become an international scientific and cultural center. In the 12th century the Mongols invaded it. The Safavid dynasty (15011722), under which the dominant religion became Shiite Islam, followed, and was then replaced by the Qajar dynasty (17941925).
Persia, as it was, had been one of the greatest empires of the ancient world, and has long maintained a distinct cultural identity within the Islamic world by retaining its own language and adhering to the Shia interpretation of Islam.