A 27-year war between two Greek superpowers was recorded as it happened

From 431 to 404 BC, the Athenian empire and the Spartan-led Peloponnesian League fought a grinding, on-and-off war for dominance over the Greek world, a conflict historian Thucydides began chronicling in its first year. He blamed it on 'the growth in power of Athens, and the alarm which this inspired in Sparta,' a line still quoted by theorists describing how rising powers provoke established ones. Athens lost most of its navy in a disastrous Sicilian expedition and surrendered in 404 BC.

— Thucydides, History of the Peloponnesian War — written c. 431-411 BC
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