Marinus was a Dalmatian stonemason who, by tradition, became a deacon and lived as a hermit on Monte Titano, the rocky height around which the small state of San Marino later grew. The surviving hagiographical accounts of his life were recorded centuries after his lifetime, so much of the detail is preserved as tradition rather than firmly documented history; the earliest manuscripts naming him date only to the 10th century. He is venerated in both the Eastern Orthodox and Roman Catholic churches and is numbered among the pre-schism Western saints.
According to these accounts, Marinus came from the island of Arba, the modern Rab off the Dalmatian coast, and worked as a stonemason. He fled the Diocletianic persecution and made his way to the region of Rimini, where he was ordained a deacon by Gaudentius, the bishop of that city. Tradition relates that he afterward withdrew to Monte Titano to live as a hermit, the synaxarion explaining his flight by the story of an unstable woman who accused him of being her estranged husband.
On the mountain Marinus established a cell and an oratory, and a community of disciples gathered around him. From this initial settlement the Republic of San Marino traces its origin, conventionally dated to the year 301; Marinus is honored as its founder, and his memory is bound up with the small state's identity. By tradition he died in the winter of about 366. His reputed parting words, 'Relinquo vos liberos ab utroque homine' ('I leave you free from both men'), are remembered as the foundation charter of San Marino's later independence.