By the 7th century, the Assyrians were using true horse archers. This is alleged to be Ashurbanipal (668 BC - c. 627 BC)
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Thanks for the reply Dan,

That horse archer being guided by another man on horseback is interesting, looks a bit like a poor mans chariot. I also got your book, i'm only ten pages in but it's really good and gave me an overview of the development and chronology of middle eastern civilizations.