Gratian

The Decretum Gratiani, also known as the Concordia discordantium canonum or Concordantia discordantium canonum or simply as the Decretum, is a collection of canon law compiled and written in the 12th century as a legal textbook by the jurist known as Gratian. It forms the first part of the collection of six legal texts, which together became known as the Corpus Juris Canonici. It was used by canonists of the Roman Catholic Church until Pentecost (May 19) 1918, when a revised Code of Canon Law (Codex Iuris Canonici) promulgated by Pope Benedict XV on 27 May 1917 obtained legal force.