From the seventh century the Canon of the Mass has remained relatively unchanged. It is to Pope Gregory I (590-604) the great organiser of all the Roman Liturgy, that tradition ascribes its final revision and arrangement. His reign thus provides a natural division in the discussion of the history of the Canon. Pope Pius V made some changes such as removing from the Canon the mention of the emperor or king and shortening the "Communicantes" prayer by removing some saints' names and some clauses of the prayer.