John Lydgate’s The Siege of Thebes, written c. 1421–22, is the only Middle English poetic text that recounts the fratricidal struggle between Oedipus’s sons Eteocles and Polynices as they contend for the lordship of Thebes. The text reflects the problem of poetic authority and the political and ethical themes of Lydgate’s poetic career in the 1420s, when he was writing as a Lancastrian propagandist and as unofficial royal poet.