In the history of canon law, the decretalists of the thirteenth century formed a school of interpretation that emphasised the decretals, those letters issued by the Popes ruling on matters of church discipline (epistolae decretales), in preference to the Decretum Gratiani (1141), which their rivals, the decretists, favoured. The decretalists were early compilers of the papal decretals, and their work, such as that of Simon of Bisignano (c. 1177), was used by the dominant decretist school.