ElectionMarcellinus is listed as a pope in the Liber Pontificalis (~885 AD); however, there is no record of him in the Martyrologium hieronymianum, the Depositio episcoporum, or in the Despositio martyrum. The Liber Pontificalis' record itself is copied from a lost text called the Acts of St. Marcellinus.
PersecutionMarcellinus' reign began during the long period of tolerance Rome had towards Christianity. The Roman Emperor Diocletian (r.284-305) upheld this tolerance, in part due to the influence of his wife Prisca, and his daughter Valeria, who both favoured certain Roman Christians. Christianity grew, while pagan leaders felt increasingly threatened.
Falling to PaganismAccording to the same Acts of St. Marcellinus text, the Liber Pontificalis reports that Marcellinus weakened, and offered sacrifices to the pagan idols. It adds however, that after a few days, he repented of his actions, and was then beheaded. Other documents speak of his defection.
Other WorksFrom an epitaph of the deacon Severus, found in the Catacomb of Callistus, it writes that new burial chambers were added in the cemetary, crediting Marcellinus.
DeathPope Marcellus I (307-309).
Marcellinus died in the second year of the persecution and, in all probability, a natural death. No trustworthy sources of the fourth of fifth century mention him as a martyr.
286-305: Eastern Roman Emperor, Diocletian
Western Roman Emperor, Maximian
296: Britain divided into 4 Roman Provinces
303-311: The Third Persecution, by Emperor Diocletian