 The "Decretum" of Gratian is already called "Corpus juris canonici" by a glossator of the 12th century, and Innocent IV calls by this name the "Decretales" or Decretals of Gregory IX.Since the second half of the 13th century, "Corpus juris canonici" in contradistinction to the Roman "Corpus juris civilis" of Justinian I, generally denoted the following collections