In certain Orthodox calendars, today is a commemoration for Pope St. Marcellinus. (In the Roman calendar his feast day is April 26.) He is an interesting figure in some ways. He was Pope during the Diocletian persecution. Diocletian seems not to have had much interest in Christians, but his son-in-law and co-emperor Galerius seems to have had a vendetta against them, which led to sporadic but intense crackdowns. Marcellinus's course of life during the persecution is almost impossible to pin down; he may or may not have sacrificed to idols to avoid persecution and he may or may not have been martyred in the persecution -- we have stories in practically every combination, none of them reliable. The Donatists insisted that he had committed apostasy to avoid persecution; Augustine seems to have thought the charge nonsense. But the Donatists are not the only ones among whom the story seems to have circulated, and it's true that Marcellinus, although he ends up venerated as a martyr (and possibly not very long after his death), is not generally listed on the early lists of martyrs; in fact there are curious cases where he's not even listed as a pope in lists of papal succession. These points may indicate that this story of apostasy was circulating in Rome, as well. Later legends try to reconcile all of this by having him first give in and then repent and be martyred; this may even be true, although we don't know. But it's also weird, if he did apostatize, that we don't know it for sure; all we have are accusations of the Donatists -- not exactly the most scrupulous of people in their ad hominems -- and some suggestions that there might have been rumors to that effect elsewhere. It's not as if it would have been a small thing. Johann Peter Kirsch's Catholic Encyclopedia article on him notes that the Roman clergy got through the Diocletian persecution with relatively few casualties, and speculates that Marcellinus may have made some deals to get exemptions, deals of which not everyone approved, which was exaggerated in some quarters to a full-blown apostasy. That would explain everything, but we don't know. All we know is that he is listed as a martyr in the calendar of saints.