Thucydides' and Herodotus' comments on a portentous (and unique) Delian earthquake contain the same phrase, but date the event almost 60 years apart and mutually rule out each other's datings. Two additional problems in these passages – geology demonstrates that Delos has never in fact had an earthquake of any significance and κινεῖν is not the word for an earthquake – point to an explanation for the historians' treatment. They are based on the Delphic oracle quoted by Herodotus which promised to ‘move unmoved Delos’, a paradox based on the island's mythical transition from floating to fixed (Pindar), but liable to confusion with its equally well-known aseismicity. Normally κινεῖν τὰ ἀκίνητα is used of interfering with religious sites; but the oracle's prediction was interpreted as an earthquake, that was assumed to have occurred in due course (although it had not). Both historians accepted the interpretation, but followed different datings since they invested it with different symbolism, Herodotus of the evils of the Persian and subsequent Greek wars, Thucydides of excited anticipation on the eve of the Peloponnesian War, since for him κίνησις meant ‘mobilization’ (1.1).