Nothing outside Zoroastrian tradition attests him. The traditional dating, which places Zarathustra 258 years before Alexander, appears to derive from an ancient confusion between this Vishtaspa and Hystaspes the father of Darius I, who is a different and later man. Linguistic dating of the Gathas places their composition many centuries earlier, in the second or very early first millennium BCE, somewhere in eastern Iran or Central Asia, which leaves the patron with no fixed place, date or external record.
What would resolve this An epigraphic, archival or archaeological find naming Vishtaspa in a datable eastern Iranian or Central Asian context, or a decisive advance in the absolute dating of Old Avestan.
OpenIranian philology; Central Asian archaeology; Avestan studiesDivinity Atlas Open Questions Register, First Edition