This chapter assesses Phlegon of Tralles’ paradoxographical works Peri Thaumasion and Peri Makrobion, and demonstrates that Phlegon’s use of source citation and other strategies of authentication in these works is designed to appeal to a range of readers and reading cultures in the cosmopolitan Roman empire. In the tradition of Greek paradoxography that dates back to the Hellenistic era, Phlegon offers many citations from literary sources for the marvels he reports; these are all Greek authors, and predominantly Hellenistic or earlier in date, and would fulfil Greek-speaking readers’ expectations for the traditions of paradoxography. Other strategies, however, seem designed to appeal to Roman expectations. Phlegon’s use of autopsy as an authenticating trope echoes what Latin authors (Mucianus, Pliny the Elder) brought to the genre. Finally, Phlegon’s citation of documents such as census records is designed to appeal to inhabitants from across the empire who would have had personal experience of Imperial record-keeping. By combining all three of these authenticating methods so that they mutually reinforce one another, and dovetail in a believable way with readers’ extratextual experiences, Phlegon updates what was originally a Hellenistic, highly literary genre for the contemporary era and his boundary-crossing readers.