Not sure if this has been mentioned before, but I was just reading History of the Peloponnesian War when I came across this beautiful quote:

This day will be the beginning of great misfortune for the Hellenes. - Melesippus, the final Spartan herald to Athens, on being rebuffed by the Athenians, 431 BC

Thucydides (edited by Robert B. Strassler, trans. by Richard Crawley), History of the Peloponnesian War (as presented within Strassler's The Landmark Thucydides), Book Two, 2.12.3