A Roman, son of Projectus (per Liberian Catalog), Marcellinus succeeded Pope Caius to the seat of Peter on June 30, 296. It was a time of peace throughout most of the Empire.
Diocletian had become emperor in 284. His policies stabilized the empire and put an end to the Crisis of the Third Century. He reorganized the government structure, established a policy of inaction towards various religions and tried to handle the inflation problem. He also fought the pesky Persians and won a peace accord.
As all these stabilizing activities improved the lives of the common people, Marcellinus saw his churches become more populous. Books were copied so that more people could read the words of the Holy Fathers. People were free to be in communities of worshippers. In 301, Armenia became the first officially Christian state. Things were looking up.
As Diocletian got older and sicker, the government began to change. They developed a four man rule. And Diocletian was the more conservative member of the four.
In the fall 302, deacon Romanus of Caesarea, a very vocal man, had his tongue removed for defying the orders of the court and interrupting official sacrifices. He was then sent to prison and eventually executed in November 303. Diocletian and his second in command, Galerius, meanwhile, shortly after dealing with Romanus, left to winter in Nicomedia. While there, still angered by Romanus' activity, they argued about the policy towards Christians. Diocletian thought that preventing Christians from being involved in governmental bureaucracy and the military would be sufficient to appease the gods. However, Galeriaus wanted total extermination. To come to a decision, they went for advice to the oracle of Apollo at Didymus. The oracle had difficulty reading the entrails of the animals so they were told that the impious on earth had hindered Apollo's ability to provide advice. Diocletian then asked for advice from the court on who were the impious. He was informed that it could only mean the Christians. This lead Diocletian to agree to universal persecution.
Christians were told to leave the military. Christian property was confiscated, including the cemeteries. Books were burned. As the Romans began to hear rumors of the persecution, they readied themselves. They blocked up the principle galleries in the Catacombs of Callixtus to prevent destruction and desecration of the dead. It was owned by the Church. But the Catacombs of Priscilla, on the Via Salaria were owned privately and could not be touched.
Unsubstantiated rumors began in the years after Marcellinus's death claimed that he had given books to be burned and that he had participated in sacrifices to the pagan gods, but there is no first hand accounts and even St Augustine, writing 100 years later, did not find it at all difficult to defend Marcellinus's valor and dignity. He claimed it was a situation of forgery and lies.
Marcellinus appeared to escape the persecution, as did most other Christians in the western part of the empire. He died, probably of natural causes, in either April or October of 304. Pope St. Marcellinus was buried in the private Catacombs of Priscilla.
Pope St. Marcellinus, pray for us.