I can recommend the writings of K. E. Eduljee who has been digging into this topic for an extended period of time. http://www.heritageinstitute.com/zoroastrian

I can recommend the writings of K. E. Eduljee who has been digging into this topic for an extended period of time. http://www.heritageinstitute.com/zoroastrianism/ http://www.heritageinstitute.com/zoroastrianism/ Scroll down to the Site Contents, the third column is dedicated to (mostly) Persian history.