St. Mark, a Roman priest, ws the right hand of Pope St. Sylvester, during the latter’s pontificate, and finally succeeded him. St. Mark’s term as Pope lasted only eight months, for he was called to his eternal reward in the year 336. Pope Damasus records of him that his life was blameless and full of love of God. He cared little for honors and despised earthly things, for his inmost heart was attached to virtue alone. He was the champion of justice and a perfect lover of Christ.
(Source: The New Roman Missal, Rev. F. X. Lasance)