Book 3 resumes the narrative of Persian expansion after the discussion of Egypt in Book 2. In this section, Herodotus describes the Persian king Cambyses’ reign, conquest of Egypt, and descent into madness; the usurpation of the Persian throne by the Magi after Cambyses’ death; and the rise of Darius to power in Persia after a coup d’etat. In two notable digressions, Herodotus recounts the careers of the Greek tyrants Polycrates of Samos and Periander of Corinth. Finally, in a geographical aside, he discusses the natural history and wealth of India, Arabia, and western Europe, arguing that the most distant lands harbor the most valuable and desirable resources.

According to the Persians, Herodotus claims, Cambyses invaded Egypt to punish Amasis for deceiving him. Prompted by an Egyptian physician at his court who was angry with Amasis, Cambyses asked for the hand of Amasis’ daughter. Amasis, suspecting Cambyses intended her as a concubine, sent the daughter of the late pharaoh Apries in her place, which rankled the Persian king. Herodotus recounts two other variants of the story, neither of which provide a political explanation for the invasion but repeat the pattern of personal revenge that often serves as historical causality in the Histories.