He was one of the seventy-two disciples (Gospel). He went to Egypt where he was the first to announce Christ at Alexandria. The preaching of the Gospel, which his martyrdom confirmed, made him to enter into glory (Secret) where St. John shows him to us as one of the four symbolical animals who attend the triumph of the immolated Lamb.
His body was taken to Venice, whose patron he is since the ninth century. Rome possesses a church dedicated to St. Mark, where a Station is held on the Monday of the third week in Lent.
Let us profit by the teaching of St. Mark who wrote the Gospel of Christ and preached it, and let us have recourse to his prayers (Collect).
Thou hast protected me, O God, from the assembly of the malignant, alleluia: from the multitude of the workers of iniquity, alleluia, alleluia. * Hear, O God, my prayer when I make supplication to Thee: deliver my soul from the fear of the enemy.
(Psalm 63:3,2 from the Introit of Mass)
Deus, qui beatum Marcum Evangelistam tuum evangelicae praedicationis gratia sublimasti: tribue, quaesumus; ejus nos semper et eruditione proficere, et oratione defendi.
O God, who by Thy grace didst raise up blessed Mark, Thy evangelist to be a preacher of the gospel; grant, we beseech Thee, that we may ever profit by his teaching and be defended by his prayers.
From the Catholic Encyclopaedia: http://www.newadvent.org/cathen/09672c.htm