According to Thucydides’ account (II, 12), the beginning of the Peloponnesian War is marked by the sentence pronounced by the Spartan herald Melesippus : «This day will be at the head of great disasters for the Greeks». This paper assesses the importance of these words in Thucydides’ work and discusses its relationship with Aristophanes’ Peace (435-436), where the same expression is employed. Furthermore, it examines the fortune of this sentence, from Homer and Herodotus to Flavius Josephus and Ælius Aristides.