St Mark, the Winged Lion

Saint Mark's symbol in art is a Lion, usually winged and this one is on the cathedral in Orvieto, Italy.
In the book of Revelation, the visionary sees about the throne of God four winged creatures: a lion, an ox, a man, and an eagle. It has customarily been supposed that these represent the four Gospel writers, or the four Evangelists.
The lion is seen to stand for Mark, whose narrative begins with John the Baptist crying out in the desert (a lion roars in the desert).