How did the city-state of Athens defeat the invaders from Persia, the first world empire, on the plain of Marathon in 490 BCE? Clever scholars skeptical of our earliest surviving source, Herodotus, have produced one ingenious theory after another. In this stimulating new book, bound to provoke controversy, Peter Krentz argues that Herodotus was right after all.

Beginning his analysis with the Athenians' first formal contact with the Persians in 507 BCE, Krentz weaves together ancient evidence with travelers' descriptions, archaeological discoveries, geological surveys, and the...