I. For more than three thousand years the name of Zoroaster has been known in the world. Yet, during the middle ages Europe was under such a cloud that his name and his precepts faded, almost, from the memory of man. It was known that Persia, until the battle of Marathon (490 B. C.) was master of Western Asia, and the doctrines of Zoroaster were dominant in her realm. But Persia, even as late as three hundred years ago, was, to Europe, almost a sealed book. With the revival of learning, however, inquiry began to be made into her ancient doctrines and their author.