It was established by Cyrus the Great and then his successors. We talked about it in previous videos, how they were able to conquer the Neo-Babylonian Empire in 539 BCE and then go on to conquer much of the Middle East, able to conquer the long-lived Egyptian Empire. And they seem somewhat unstoppable at this point, in 490 BCE. 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.