At this point, we have Darius is ruler of the Persian Empire, the Achaemenid Empire, as it's often referred to. And they're able to keep expanding until they come across some unexpectedly resistant people, and that's the Greeks. And this is probably one of the most famous and legendary stories in history, the rivalry, the conflicts between the Persians and the Greeks. And you should maybe take it with a little bit of grain of salt, because what we know of it, the history that I'm about to give you, comes to us from Herodotus. And Herodotus, who's often known as the father of history, he was Greek, and he also lived after a lot of these conflicts happened, and he wrote about these conflicts. His adult life was well after these happened, so he had to talk to people who were around that time. And obviously, he is getting the Greek side of the story.