No empire in history, as far as we can tell, has ever had such a large fraction of the world's population under its control. And so that gives you a sense of, I guess you could say, how great or how large an empire this was. Now Darius the Great, he is also famous, especially from a Greek perspective, for going after the Greeks. You had these Greek revolts in these towns on the west coast of the Anatolian Peninsula. They revolted against their Persian overlords, I guess you could say, and they did that with the help of the Athenians. And so Darius didn't like this. In the 490s, he starts going after the Athenians.