Cyrus took his nomadic warriors and conquered most of Mesopotamia, including the Babylonians, which ended a sad period in Jewish history called the Babylonian Exile, thus ensuring that Cyrus got great press in the Bible. But his son Darius I was even greater. He extended Persian control east to our old friend the Indus Valley, west to our new friend Egypt, and north to crash-course newcomer Anatolia. By the way, there were Greeks in Anatolia called Ionian Greeks who will become relevant shortly. So even if you weren't Persian, the Persian Empire was pretty dreamy. For one thing, the Persians ruled with a light touch, like conquered kingdoms were allowed to keep their kings and their elites as long as they pledged allegiance to the Persian king and paid taxes, which is why the Persian king was known as the King of Kings. Plus taxes weren't too high and the Persians improved infrastructure with better roads and they had this pony express-like mail service of which Herodotus said, They are stayed neither by snow nor rain nor heat nor darkness from accomplishing their appointed course with all speed.