This dissertation analyzes Senecan drama through the malleable figure of the vates, which has the dual resonance of poet and prophet. Both types of vates transmit fatum, but in Seneca, where prophets prove unsuccessful, poets have greater interpretive capacity and greater autonomy. The dissertation is structured along three vertical' levels of prophetic activity: Olympian, infernal, terrestrial. Chapter 1 articulates the ways in which traditional prophets (Calchas, Tiresias, Manto, and Cassandra) are flawed in Senecan tragedy. Where these Olympian prophets fall short, the various non-prophet' figures who assume the vatic role prove more successful. Chapter 2 argues that Seneca's infernal figures (ghosts and furies) usurp the functions of the vates by communicating the knowledge of the underworld to those on earth. Yet they can only appear for brief periods of time and are powerless to intervene directly in human affairs, as is the case with the Furia and with the ghosts of Laius, Thyestes, Hector, and Achilles. Chapter 3 focuses on three species of human non-prophet figures: (1) the avenger'-vates Atreus and Medea, who elide the role of prophecy altogether, since they style themselves as deities and as authors; (2) the accidental' prophet (for example, Andromache), who utters statements that he or she does not realize will prove true; (3) the vatic destabilizers Astyanax and Polyxena. These vatic analogues, along with the Juno-Hercules pair (Chapter 4) subvert and create fatum in ways that reveal their poetic links, specifically, the unpredictable (and so, powerful) qualities of authorial innovation. A case study of the vates, Oedipus, is the focus of Chapter 5. Seneca uses Oedipus' problematic relationship with oracles to explore issues of the self and of causality. Prophecy's goal is to isolate a single answer. Prophecy in Senecan tragedy fails, I propose, due to multiplicity in the areas of timescale, sites of knowledge, and cause. Neither poets nor prophets ultimately have full control over the future. But Seneca's limited prophets, when counterposed with his more successful poet characters, dramatize how the poet, who has access to more flexible forms of meaning, also has greater autonomy at understanding and creating fatum.