A large number of the most informative fragments of the Hellenistic Greek historians are transmitted by Athenaeus. Unlike the frequently jejune evidence provided by scholiasts, lexicographers and the like, these texts allow us to draw historiographical conclusions about lost writers: on this basis, scholars have posited, for example, the place of a given author in the Hellenistic ‘schools’ of history. The importance of Athenaeus as a source for history-writing between Xenophon and Diodorus calls for detailed study of the Deipnosophist's method of citing these lost authors. The present article focuses on Athenaeus' testimony concerning the downfall of Archaic Sybaris through luxury and excess in order to show that certain phrases, sentence patterns and even trains of thought can be reliably identified as belonging to Athenaeus rather than the cited authority. This discovery entails surprising results: traditions ascribing the destruction of Sybaris to morally corrosive luxury are late and of little historical value. More generally, the debilitating effects of luxury cannot serve as an exemplum supporting the claim that Hellenistic writers tended to explain historical events through moral causes; apparent evidence for this causal nexus is better assigned to Athenaeus than to the historians he names. In view of these conclusions, a cautious reassessment of all Athenaeus’ testimony on fragmentary historians is appropriate.