And this, as the prophet foretold, is the greatest symbol of His power and role; as is also proved by the things which fall under our observation. For consider all the things in the world, whether without this form they could be administered or have any community. For the sea is not traversed except that trophy which is called a sail abide safe in the ship; and the earth is not plowed without it: diggers and mechanics do not their work, except with tools which have this shape. And the human form differs from that of the irrational animals in nothing else than in its being erect and having the hands extended, and having on the face extending from the forehead what is called the nose, through which there is respiration for the living creature; and this shows no other form than that of the cross.
Justin Martyr
First Apology
Chapter LV