 Book IX begins with a refutation of the heresy of Noetus.In this particular error, Hippolytus implicates the now-canonised popes Zephyrinus and Callixtus I.This theme of Hippolytus' conflict with the papacy is expanded upon in the second chapter of Book IX, which deals in particular with the errors of Pope Callixtus, whom Hippolytus identifies as a "sorcerer".