Kanishka III is known from only one inscription, known as the Ara inscription for the place where it was found, near the town of Attock in what is now Pakistani Punjab.
The inscription is on a piece of stone and records, in Kharoshthi script, the digging of a well in the year 41, during the reign of Maharaja Rajatiraja Devaputra Kaisara
Kanishka, son of Vajheshka. This Vajheshka is taken to be the same as Vasishka, who we know was ruling just prior to this time.
No coins have as yet been definitively attributed to Kanishka III.