Köln, Erzbischöfliche Diözesan- und Dombibliothek 115, fol 2r

Collectio canonum Dionysio-Hadriana

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After Gratian compiled his Decretum, jurists collected papal decretals.  These decretals contained the decisions of the papal curia for cases that had been appealed to Rome.  These collections began as appendices attached to manuscripts of the Decretum.  By the fourth quarter of the twelfth century, they were organized into five books

Iudex, Iudicium, clerus, connubia, crimen (Judge, Courts, Clergy, Marriage, Criminal Law)

and arranged according the subject matter.  This format became standard for the codification of decretals until 1917.