The Iranian Empire proper begins in the Iron Age, following the influx of Iranian peoples. Iranian people gave rise to the Medes, the Achaemenid, Parthian, and Sasanian Empires of classical antiquity.
Once a major empire, Iran has endured invasions too, by the Macedonians, Arabs, Turks, and Mongols. Iran has continually reasserted its national identity throughout the centuries and has developed as a distinct political and cultural entity.
The Muslim conquest of Persia (633–654) ended the Sasanian Empire, and was a turning point in Iranian history. Islamization of Iran took place during the eighth to tenth centuries, leading to the eventual decline of Zoroastrianism in Iran as well as many of its dependencies. However, the achievements of the previous Persian civilizations were not lost but were to a great extent absorbed by the new Islamic polity and civilization.