Walter M. Miller, Jr., A Canticle for Leibowitz (1956)

“And again: Vexilla regis inferni prodeunt… Forth come the banners of the King of Hell, whispered memory of that perverted line from an ancient commedia. It nagged like an unwanted tune in his thought.”  (Part Two, Fiat Lux, p. 143 in the Bantam edition of 1988).