Shaka is the Indian term used for the people called Scythians, who originally belonged to central Asia.
Defeated by their neighbours the Yueh-chis (the tribal stock to which the Kushanas belonged) they gradually came to settle in northwestern India around Taxila in the first century B.C
Under the successive Shaka rulers their territories extended up to Mathura and Gujarat.
The most famous of all the Shaka rulers was Rudradaman who ruled in the middle of second century AD. His empire was spread over almost whole of western India. His achievements are known through the only inscription that he got engraved on a boulder at Girnar or Junagarh.
This inscription happens to be the first royal inscription of early India composed in chaste Sanskrit.