A prime example that fact is stranger than fiction. Vidal has an ability to take what is known and to take the stories that we believe we already know and to tell them to us in a way that turns them from stories to reality.
You read a book of his (in this case, Creation is) a stunning glimpse into a life that neither the author nor the reader has lived in or experienced or even has heard primary accounts of. Yet the author takes the reader by the hand, throws them into this world, and just spins such a beautiful tale that by the time you're finished it, you find yourself feeling like you're an expert on the subject. It's not because he plied you with historical facts. It's because he makes you feel like you are living in this world.
I feel like I was living amongst the Bactrians and the Indians and the ancient Chinese. It truly was a really, really, really great read. He blurs the line between fact and fiction so beautifully that, on one hand, I doubt everything he says because to infuse the characters and the story with such personality, you have to take liberties with the facts. On the other hand it's so historically right that even if the facts aren't true, you can't help but think that the way he describes these actions as occurring has to have been close to how that happened.
I imagine that Xerxes would read this book and laugh from joy as opposed to ridicule.