In his Praefatio Livy identifies the principal purpose of historiography in the exempla which it provides to the reader. However, a comparison between the exempla used by Livy's characters in public speeches and the version of the same episodes previously given by the historian shows his awareness of the ambiguity inherent in the historical exemplum, when it is used for rhetorical purposes. This awareness problematises Livy's relationship with Augustus' cultural programme, which exploited historical exempla as a fundamental means of communication.