Josephus The Facetious.

'3.  Now there was about this time Jesus, a wise man, if it be lawful to call him a man; for he was a doer of wonderful works, a teacher of such men as receive the truth with pleasure. He drew over to him both many of the Jews and many of the Gentiles. He was [the] Christ. And when Pilate, at the suggestion of the principal men among us, had condemned him to the cross , those that loved him at the first did not forsake him; for he appeared to them alive again the third day , as the divine prophets had foretold these and ten thousand other wonderful things concerning him. And the tribe of Christians, so named for him, are not extinct at this day.'
(Not a believer - this Jew worked for the Emperor Vespasian and was considered a traitor. His tone is obviously mocking but it gives a clear, independent source of the basic origins of Christianity.)
You really would not believe the lengths that atheists have gone to in FAILING ABSOLUTELY to undermine this. There have been wild claims of: additions, distortions, Christian dishonesty. Funny how they only ever go onto this level of attack when cornered, innit?