Book 5 begins by describing the Persians’ subjugation of the Thracians and their Greek neighbors living on the northern coast of the Aegean Sea after Darius’ failed campaign against the Scythians. The focus of the Book, however, is the revolt of the Ionian Greek city-states against Persia, which occurred between 499-494 BCE. The Ionian cities sought aid from Athens and Sparta during the rebellion, and Herodotus’ narrative of the revolt also includes a summary of the histories of Sparta and Athens during the latter half of the sixth century BCE. These digressions describe the overthrow of the Pisistratid tyranny and the establishment of democracy in Athens, as well as Sparta’s machinations to influence the Athenian government during these years.

After Darius returned to Asia, the Persians remaining in Europe under Megabazus subdued the Greek settlements on the Hellespont and conquered all the tribes inhabiting Thrace. Herodotus claims that Thrace (a region now occupied by modern Bulgaria and European Turkey) is the most populous nation in the world, other than India. He asserts that Thrace would be the most powerful country if it were able to achieve political unity, but is incapable of doing so.