The Cambridge History of India, Vol. I: Ancient India v1.c3.13

v1.c3.13

In the same way, the later name of the era of 78 a.d. may be due to its use for centuries by the Çaka satraps of Western India; but they can scarcely have founded this era. Their very title ‘satrap’ shows that they were originally feudatories; and they were most probably feudatories of the Kushāṇas. If so, they would use the era of their suzerains as a matter of course.