I recently crossed paths with a fascinating article from the Centre for Public Christianity regarding the earliest images of the cross. While historical research has shown that depictions of the cross in church decorations and jewelry did not become prevalent until after the fourth century, there were actually symbolic likenesses of the cross as early as 200 AD in papyrus manuscripts of the New Testament.
According to the article, scribes "took the letter ‘t’ (written in Greek as Τ) and the letter ‘r’ (written in Greek as Ρ) and ingeniously laid them on top of each other to form what looks like a man on a cross. The image below is from a manuscript of Luke’s Gospel known as P75, dated to about AD200. The ‘staurogram’, as it is called, is clearly visible."
The image of the cross is everywhere in Christian society today, but it's nice to see that the symbolism goes back further than we previously were taught. You can read the article in its entirety here: http://publicchristianity.org/opinion/the-first-image-of-the-cross#.VJ0fhsAEN
