This article investigates how Greco‑Roman literature constructs a “literary jurisprudence” of incest, with particular focus on Oedipal incest. After reviewing the scant and conflicting treatment of incest by Greek philosophers and tragedians, it argues that Seneca, in his Oedipus, is the first Roman author to formulate an explicit interdiction of mother–son incest, presenting it as a miasma and as the gravest violation of the Naturae lex, in clear contrast both to Sophocles and to ancient positive jurisprudence, but, strikingly, this strong condemnation of incest is not found in Seneca’s philosophical works.