Summary: St. Marcellinus, a priest, was beheaded alongside St. Peter an exorcist, during the persecution of Christians by Diocletian. Pope St. Damasus was told the following story from their executioner, Dorotheus.
The two saints saw their imprisonment as an opportunity to evangelize and converted their jailer, his wife and daughter. The jailer and his family were crushed to death while Marcellinus and Peter were led to the forest and told to clear brambles from the place of their execution. They were beheaded secretly and their bodies hidden so they would not be venerated. The executioner eventually repented of the killing and became a Christian. He led devout Christians to the remains which were then buried in the catacomb of St. Tiberius. Pope Gregory IV sent the relics to Frankfurt, Germany in 827 believing that the relics would bring blessings to the Church of Germany. Saints Marcellinus and Peter are included in the Roman Canon.