Saint Pope Sylvester I †335) was the bishop of Rome from 31 January 314 until his death. He filled the See of Rome at an important era in the history of the Western Church, yet very little is known of him. The accounts of his pontificate preserved in the seventh- or eighth-century Liber Pontificalis contain little more than a record of the gifts said to have been conferred on the church by Constantine I, although it does say that he was the son of a Roman named Rufinus. His feast is celebrated as Saint Sylvester's Day, on 31 December in Western Christianity, and on 2 January in Eastern Christianity.
Saint Pope Mark I (†336) was the bishop of Rome from 18 January to his death. Little is known of Mark's early life. According to the Liber PontificalisMark succeeded Sylvester I as pope on 18 January 336. Some evidence suggests that the early lists of bishops and martyrs known as the Depositio episcoporum and Depositio martyrum were begun during his pontificate. According to the Liber Pontificalis, Pope Mark issued a constitution investing the bishop of Ostia with a pallium and confirming his power to consecrate newly elected popes. Likewise, according to the Liber Pontificalis, Pope Mark is credited with the foundation of the Basilica of San Marco, a basilica in Rome, and a cemetery church over the Catacomb of Balbina, just outside the city on lands obtained as a donation from Emperor Constantine. Mark died of natural causes on 7 October and was buried in the catacomb of Balbina. In 1048, his remains were removed to the town of Velletri, and from 1145 were relocated to the Basilica of San Marco in Rome, where they are kept in an urn under the altar. His feast day is celebrated on 7 October.