From the inscriptions of Nabonidus we learn that Cyrus, king of Anshan (Susiana), began war against him in 553 B.C.; in 550, when Astyages marched against Cyrus, his troops rebelled, and he was taken prisoner.
It appears to have denoted the territory above Babylonia stretching from Anshan in the southeast north-westwards, across the Tigris-Euphrates district, indefinitely towards Asia Minor.
Anshan is a district of Elam or Susiana, the exact position of which is still subject to much discussion.
The Pasargadian kings of Anshan were vassals of the Median empire.
And Cambyses I., "kings of Anshan," and the same title is given to him in the inscriptions and in the chronicle of Nabonidus of Babylon before his victory over Astyages.