Lives of the Saints, by Alban Butler, Benziger Bros. ed. [1894], at sacred-texts.com
ST. MARK was by birth a Roman, and served God with such fervor among the clergy of that Church, that, advancing continually in sincere humility and the knowledge and sense of his own weakness and imperfections. he strove every day to surpass himself in the fervor of his charity and zeal, and in the exercise of all virtues. The persecution ceased in the West, in the beginning of the year 305, but was revived a short time after by Maxentius. St. Mark abated nothing of his watchfulness, but endeavored rather to redouble his zeal during the peace of the Church; knowing that if men sometimes cease openly to persecute the faithful, the devil never allows them any truce, and his snares are generally most to be feared in the time of the calm. St. Mark succeeded St. Sylvester in the apostolic chair on the 18th of January, 336. He held that dignity only eight months and twenty days, dying on the 7th of October following. He was buried in a cemetery in the Ardeatine Way, which has since borne his name.
Reflection.—A Christian ought to be afraid of no enemy more than himself, whom he carries always about with him, and from whom he is not able to flee. He should therefore never cease to cry out to God, "Unless Thou, O Lord, art my light and support, I watch in vain."