Thucydides inserted the Pentecontae

Thucydides inserted the Pentecontaetia or narrative of the Fifty Years into book 1 (1.89–118) chiefly to buttress and elaborate his judgment on the true cause of the war. Its stated purpose was to survey the growth of Athens’s power during the period between the Persian and the Peloponnesian Wars, and it starts with a sentence that connects its subject with the earlier statement in 1.23 of the war’s true cause: “How the Athenians rose to greatness I will now proceed to describe” (1.89). As a further reason for discussing this half-century, the historian also mentions its neglect by previous writers except for one, Hellanicus, who treated it very briefly and made chronological errors (1.97).