Cyrus of Persia conquered the Median overlords and formed the Persian Empire in 550 B.C. The victory over King Astyages and the capture of the Median capital, Ecbatana, marked the beginning of the Achaemenid Empire.
Cyrus II, later known as Cyrus the Great, was originally king of Anshan in southwestern Iran. He rebelled against Median authority around 553 B.C. Ancient accounts describe a conflict in which parts of the Median army eventually defected to Cyrus. After Astyages was defeated, Cyrus took control of the Median kingdom and incorporated its territories and political institutions into his expanding realm.
The date is conventionally given as 550 B.C., although the precise sequence of events is reconstructed from incomplete ancient evidence. Cyrus then continued expanding westward and eastward, conquering Lydia and Babylon. His successors, especially Darius I, greatly enlarged the empire, which became one of the largest states of the ancient world.