Communion Antiphon, Jn 16:7: I tell you the truth, it is for your good that I go; for if I do not go away, the Paraclete will not come to you, says the Lord, Alleluia. Saints Peter and Marcellinus are two Roman martyrs who suffered under the Diocletian persecution, about the year 303; the first was an exorcist, the second a priest. Their cultus was so important that after peace was restored to the Church, Constantine built a basilica in their honor. Their names are mentioned in the Canon of the Mass (Eucharistic Prayer I).