Marcellinus was a priest and Peter an exorcist in Rome’s Christian community. They were arrested and imprisoned during a persecution by Emperor Diocletian. In prison, they converted many people, including their jailer and his family. They were condemned to death and beheaded, supposedly in secret, in a nearby wood. But their executioner disclosed the deaths after his conversion.
Pope St. Damasus I wrote an epitaph for their tomb, over which Emperor Constantine later built a church in which he buried his mother. This pope also reported that he learned the details of their martyrdom from the executioner himself. Marcellinus and Peter are among the saints named in the Roman Canon of the Mass.