The Iron Chariots Wiki puts it, I would say, mildly:
Nothing even approaches an eyewitness account. There is no other real evidence beyond written accounts. Even the name "Jesus" is contrived. Elements of Christianity existed centuries before the alleged birth of Christ.Today, there exists little in the way of historical documentation for Jesus' life beyond the Biblical Gospel, and it is likely that these accounts were not written by eyewitnesses. This lack of evidence makes it very difficult to discern actual historical facts behind the Christian stories that describe him. This, however, has not stopped scholars from defending the existence of a historical Jesus, as well as specific views of who Jesus was.Some atheists consider discussion of a historical Jesus to be a red herring and argue that, while a person named Jesus may or may not have existed, there is clearly no reason to believe that he had special powers, was the son of God, or performed miracles. Even if it could be firmly established that Jesus, the man, existed, this would not be evidence for the extraordinary claims that make up the foundation of the Christian religion.
Authors Richard Carrier [blog] [wiki] [YT], Robert M. Price [blag] [wiki] [YT], David Fitzgerald [YT] [book], Bart Ehrman [blag] [wiki] [YT] make the case clear in their books, lectures, debates, etc. READ THEIR SHIT and THEN talk to me about the arguments (or at least watch the YT links - they're entertaining, I swear).
Anyway, the analogy I like to use regards the Roman invasion of Gaul by Caesar's 13th legion. Imagine for a moment that archaeologists stumbled upon a collection of letters signed by identifiable members of the Roman military at the time of the battle of Alesia. They are eyewitness accounts, written in first person (you may argue that the fact that the original gospels were reproduced is in fact evidence of their truth value, since apologists like to have it both ways). They consistently describe an event in the midst of the battle wherein the goddess Athena descended and gave the general a magic wand, which he used to turn various Gallic warriors into frogs. We would not expect much other evidence (beyond reproductions of this account in other places - assume there are if you want), as the remains of the frogs would have long since disappeared. We know the battle really took place, already. We already know that Caesar was a real man, too. Would this alone convince you that the goddess Athena really exists, and that magic wands exist? For some of you, it may be. If so, I may have to talk to you about an amazing investment opportunity.
But this evidence is FAR better than the evidence for the existence of Jesus Christ. There are no eyewitness accounts, let alone signed, let alone by identifiable figures referenced in other sources, let alone originals, etc. It's special pleading to accept the Gospels as accurate. It's about as justifiable as accepting any other religious text, for that matter.
There is one good argument for an actual historical Jesus (hence the qualifier "probably"). Cults spring up based on charismatic leaders who are merely human but are attributed supernatural aspects all the time. David Koresh is still worshiped as a messiah. Sathya Sai Baba is considered by millions to be God right now. True divine nature does not seem to be a prerequisite for widespread belief/adherence. But at the core of each cult/religion (the only difference is size, really) is a real person. The only difference is that the antiquity of Christianity naturally makes its history murky. I think, however, the answer lies in the similarity between early Christianities and other cults at the time, most of which were probably fabricated wholecloth as a metaphor for the sun and the zodiac signs etc. anyway, like Mithras. Much of the Gospel story seems contrived [read the Incredible Shrinking Son of Man] anyway.
The most interesting theistic argument I've heard to account for the success of other cults similar to Christianity at the time (suggesting there was a need for such an argument) is that the miracles performed by members of pagan cults were in fact real, but the work of the devil [read Not the Impossible Faith by Richard Carrier]. Anyone willing to entertain this kind of theology has lost the argument, in my mind, based on the nature of the devil in such a theology. That's another discussion.
More on the topic
Take care, sir.