Peoples speaking an Indo-European languagewho settled in Iran in the second millennium B.C. By the beginning of the first millennium, they spread westward to the Zagros, where they formed their first state, the Median kingdom (c. 720–550), with the capital at Ecbatana. After the elimination of Elam, they became a powerful force in western Iran, which was instrumental in bringing down the Neo-Assyrian empire. The Medes were in turn ousted by another Persian dynasty, that of the Achaemenids (550–330). After the conquest of Alexander the Great and the subsequent rule of the Seleucids over Iran, new Persian polities formed, first the Parthians with the Arsacid Dynasty, and then the Sassanians (A.D. 224–642).
Historical Dictionary of Mesopotamia. EdwART. 2012.