And they're so closely linked, especially because they're giving history of essentially this fifth century BCE, that this is actually a double bust of the two, Herodotus and Thucydides. So once again, a lot of the story that I'm about to tell is coming via Thucydides. So as soon as the Persians, they've been defeated, they leave, you might remember that the Athenians had to escape to Salamis. That's where you also had the naval route of the Persian navy. And so the Athenians decide, hey, let's move back to Athens. And in deciding to move back to Athens, right over there, they say, okay, well, we want to build a wall around Athens in case anyone else wants to invade us. And you might say, okay, maybe they're somewhat concerned about the Persians, but you could also argue that they're somewhat concerned about the Spartans, who are famous for having this very powerful army.