The western Satraps of Ujjaini belonged to the Kardamaka line, the earliest member of which was Yasmalika. The name Yasmalika is a Scythian name. The Kardamaka Kshatrapas of Ujjaini were the greatest rivals of the later Satavahana Empire. In Bana’s Harsha Charita Yasamalika has been described as a Saka King, which indicates that the Satraps of Ujjaini were virtually independent rulers. The name Kardamaka was derived from the river named Kardama, in Persia.
Chastana was the son of Yasmalika and started his rule. According to Dubreuil, Chastana was the founder of the Saka era. But this view has been universally rejected, for the date of Chastana according to most of the scholars was 130 A.D. Roy Chaudhuri, Rapson and Bhandarkar are of the opinion that Chastana was the viceroy of some Kushana King. The use of Kharosthi script on his coins, instead of Greek ion the obverse and Kharosthi on the reverse also lead to the conclusion that Chastana was a viceroy.
On the evidence of an inscription we come to know that Chastana ruled conjointly with his grandson Rudradamana, son of Jayadamana. It is supposed that Jayadamana predeceased his father Chastana.