Michael J. Kruger, who authors Canon Fodder has beaut little article on the earliest record we have about the Gospel / s being written. He quotes Aristides, a converted Athenian philosopher, who wrote an apology to emperor Hadrian around 125 A.D.
The Christians, then, trace the beginning of their religion from Jesus the Messiah; and he is named the Son of God Most High. And it is said that God came down from heaven, and from a Hebrew virgin assumed and clothed himself with flesh; and the Son of God lived in a daughter of man. This is taught in the gospel, as it is called, which a short time was preached among them; and you also if you will read therein, may perceive the power which belongs to it. This Jesus, then, was born of the race of the Hebrews; and he had twelve disciples in order that the purpose of his incarnation might in time be accomplished. But he himself was pierced by the Jews, and he died and was buried; and they say that after three days he rose and ascended to heaven (Apol. 2).
Michael concludes his article stating that: “Once again, we can see that core Christian beliefs were not latecomers that were invented in the fourth century (or later), but appear to have been in place from the very beginning.”
I highly recommend that you jump over to his blog and have a read for yourself.