Gratian, Concordia discordantium canonum, Barcelona, Arxiu de la Corona d'Aragon, Ripoll 78, fol. 17r

John T. Noonan, Jr. "Gratian Slept Here: The Changing Identity of the Father of the Systematic Study of Canon Law," Traditio 35 (1979) 145-172

p. 172: "To conclude, we have reason to believe that Gratian composed and commented upon a substantial portion of the Concordia. In such composition and commentary he revealed himself to be a teacher with theological knowledge and interests and a lawyer's point of view. He worked in Bologna in the 1130s and 1140s. Beyond these conclusions, we have unverified hearsay, palpable legend, and the silent figure in the shadows of S. Marco."