For all the ostensible detours, then, the first four and a half books of the Histories lay a crucial foundation for the reader’s experience of the war between Persia and Greece. The latter is not the “real” story that Herodotus has to tell, saddled with a ponderous, if amusing, preamble, but, rather, the carefully prepared culmination of a tale that grows organically from the distant origins of Persia’s expansionism to its unimaginable defeat. In the light of this structure, it is increasingly evident that Herodotus’ real subject is not so much the improbable Greek victory as the foreordained Persian defeat. But why foreordained? What, exactly, did the Persian empire do wrong?

For Herodotus, the Persian empire was, literally, “unnatural.” He was writing at a moment of great intellectual interest in the difference between what we today (referring to a similarly fraught cultural debate) call “nature vs. nurture,” and what the Greeks thought of as the tension between physis, “nature,” and nomos, “custom” or “law” or “convention.” Like other thinkers of his time, he was particularly interested in the ways in which natural habitat determined cultural conventions: hence the many so-called “ethnographic” digressions.

This is why, with certain exceptions, he seems, perhaps surprisingly to us, to view the growth of the Persian empire as more or less organic, more or less “natural”—at least, until it tries to exceed the natural boundaries of the Asian continent. A fact well known to Greek Civ students is that the word barbaros, “barbarian,” did not necessarily have the pejorative connotations that it does for us: barbaroi were simply people who didn’t speak Greek and whose speech sounded, to Greek ears, like bar-bar-bar. So it’s suggestive that one of the very few times in the Histories that Herodotus uses “barbarian” in our sense is when he’s describing Xerxes’ behavior at the Hellespont. As the classicist James Romm argues, in his lively short study “Herodotus”, for this historian there is something inherently wrong and bad with the idea of trying to bleed over the boundaries of one continent into another. It’s no accident that the account of the career of Cyrus, the empire’s founder, is filled with pointed references to his heedless treatment of rivers, the most natural of boundaries. (Cyrus dies, in fact, after ill-advisedly crossing the river Araxes, considered a boundary between Asia and Europe.)