According to the First 3rd of the Documovie ‘Zeitgeist’ that made the assertion that Jesus Christ had never actually existed and was a form of Deity made up to Worship the Power of the Sun comparing JC’s Characteristics with other Paganistic Pantheon’s Sun Gods pointing out how similar they are.
Whether a man called Jesus really existed, was crucified by the Romans and whence a religious movement sprang be historical or not is one question, the doctrine, symbolism and theology that was built up around this afterwards is another. It would not surprise me at all if there were indeed syncretism during the development of early Christianity, but the latter does not refute the former per se. If this were the case, many “historical” figures would end up confined to the realms of mythology owing to the legends that grew up around them afterwards.
So how did Tactus establish that Jesus Existed and was Crucified?
Well, Tacitus was a well-educated, high-ranking Roman senator with access to Roman state archives that were generally off limits. His reference to Christ is more of a passing comment within the context of the persecutions under Nero – events which did happen – and he is generally considered to be a careful and methodical historian for his times. I don’t see what need Tacitus would’ve had to invent something, or include it in his careful historical works if he were unsure of its accuracy, all the more since he probably wouldn’t have considered the Christians or their movement particularly important anyway – probably just seen as yet another “curiosity” from the outer reaches of the Empire to a Roman of his day.