Philosophers in antiquity met with all kinds of gruesome ends: Heraclitus covered himself in hot dung as part of an ill-advised cure for dropsy, Empedocles leapt into the crater of Mt Etna, and Chrysippus famously died of laughter, having watched his donkey attempt to eat a fig. But it seems that Hippasus of Metapontum, drowned by shipmates during a fishing trip in the Gulf of Taranto, is the only one to have been murdered for a profoundly unsettling mathematical discovery.