CANON, ROMAN. The Roman eucharistic prayer is called canon actionis by the old Gelasian sacramentary Mohlberg, Liber sacramentorum, 183. The Eucharist is an action regulated by a canon. The Roman Canon has preserved the expression infra actionem for the parts known as Communicantes and Hanc igitur. The idea of observing a canon as the norm of action in the celebration of the Eucharist was formulated by St. Augustine: Totum illum agendi ordinem quem universa per orbem servat Ecclesia He the Apostle prescribed in its entirety the order observed by the universal church throughout the world Ep. 54,6: PL 33, 203; Pope Vigilius, in a letter to Profuturus of Braga, gives the name canonica prex to the unchangeable part of the Roman eucharistic prayer. The 6th-c. Ordo Romanus I speaks of the canon without a preface Andrieu, Les Ordines Romani, 95, a practice which contradicts the oldest tradition. For Cyprian, the preface and the rest of the eucharistic prayer form a unity: Ideo et sacerdos ante orationem praefatione praemissa parat fratrum mentes dicendo: sursum corda, ut dum respondet plebs: habemus ad Dominum, admoneatur nihil aliud se quam Dominum cogitare debere Thus also the priest, by way of the preface before his prayer, prepares the minds of the brothers saying: Lift up your hearts, so that when the common people respond We have lift them to the Lord, let him be admonished that he himself ought to be thinking nothing other than about the Lord De dom. Ghana Subway Map orat. 31: CSEL 3, 289, 14- 17. The change could have been caused by the fact that, from the 4th c., only the prefaces became interchangeable, while the rest of the canon, except for certain embolisms, remained fixed.