pope probably from 291/296 to 304, although the dates of his reign, as well as those of his predecessors Eutychianus and Gaius, are uncertain. His pontificate saw a long, tranquil period terminated by a renewed and bloody persecution of Christians, the last of its kind, by the Roman emperor Diocletian. It is believed that Marcellinus became an apostate during the persecution, offering incense to the pagan gods of Rome. St. Augustine of Hippo, however, discredits the charge. Marcellinus supposedly repented and was martyred, but his martyrdom is unproved.

A long period of crisis in the government of the church followed Marcellinus' death. Because of his alleged apostasy, peace was disturbed and was not restored until the election of Miltiades in July 311.