Zoroastrianism has always commanded interest way beyond the circles of its actual adherents. Its unbroken history and distinctive beliefs span three millennia, making it one of the world's most venerable faiths and also a tradition whose ideas have found favor elsewhere. The Three Magi of the New Testament most probably were Zoroastrian priests from the Iranian world; while the enigmatic figure of Zarathushtra (or Zoroaster) himself has exerted continual fascination in the West, influencing the thought of creative artists as diverse as Voltaire, Nietzsche, Yeats and Mozart (whose opera The...