Going back to the things that don't fit, for me one of those is the idea of developing a personal relationship with God. The Jesus of the bible raised this as one of the most important things to do, that we come to know God, based on love, and do so with no other human intermediaries or location affecting that relationship. Doing that first, all things (including knowledge) would be given was the basic premise.
I can only see that following that advice would just create an independence of external human authority, or anyone claiming to have authority over us. It would pretty much strip back the credence of needing human authority at all, so it's hard for me to see why that would be included in the story for a political agenda. From what I know it doesn't fit Caesar's life / views or aligns directly with any other main religious practice at the time too.
For what it's worth though, it's just one aspect that stands out for me and there's likely other ways to look at it, I just haven't come across them yet on this point.
Well, actually, it does fit Caesar. It was widely known that anyone could come to Caesar and ask for refuge and he would give it. It was even advertised. His temples were places where a person could go and while there, they could not/would not be violated. Not hard to see how that condition that he gave out to everyone in life would be considered to be a condition that they could seek from him "with the gods" once he was "in the sky".
A lot of that sort of thing is discussed in Divus Iulius by Weinstock.
Another thing is that, as I've been going through the history, I've found quite a few stories and sayings elsewhere that have been incorporated.
First of all, there are the Stoic tales and sayings that I've already mentioned in HoM. Each time I found a comparison, I mentioned it there. Of course, at the time, I was still thinking that "Jesus" was some sort of Cynic/Stoic and these stories that belonged to other Cynics and Stoics were just collected around the "Jesus person." And it's probably true that they were utilized that way - only around the "empty place" that Caesar used to occupy.
Then, there is a snippet of a speech by Gaius Gracchus which obviously appears in modified form in the NT as a saying of Jesus:
The wild beasts that roam over Italy have every one of them a cave or lair to lurk in; but the men who fight and die for Italy enjoy the common air and light, indeed, but nothing else; houseless and homeless they wander about with their wives and children. And it is with lying lips that their imperators exhort the soldiers in their battles to defend sepulchers and shrines from the enemy; for not a man of them as an hereditary altar, not one of all these many Romans an ancestral tomb, but they fight and die to support others in wealth and luxury and though they are styled masters of the world, they have not a single clod of earth that is their own.
The whole relationship between the "scribes and pharisees" and Jesus ranting at them is right there in the relationship between Caesar as the champion of the people and the optimates/oligarchy. One figure stands out as an example of one who is like a white tomb on the outside, but inside, filthy and full of rottenness: Cato. We know that Caesar wrote a condemnation of Cato but it has not survived. Perhaps it did, in the NT.
Then, there is something attributed to Catiline that infuses a few "sayings of Jesus":
…no faithful champion of the wretched could be found except one who was himself wretched; that those who were down and out ought not to trust the promises of the solvent and the fortunate; so let those who wished to refill their empty purses and recoup their losses see what debts, what possessions, what daring he himself had; that he who was to be the general and standard-bearer of the unfortunate should himself be least timid and most unfortunate.
I suspect that once the Caesar items have all be matched, what is left will be found among the Stoics, Cynics, and other popular heroes of Rome.
The book of Matthew is something else. I think Atwill is right: it was composed by Josephus using Mark and some other materials. At that point, Jerusalem had already been destroyed - and I'm not entirely sure it was done by the Romans alone, though they took credit. There are a couple of references to a comet including in Tacitus.
The thing is, unless a person has a whole lot of bits and pieces floating around in their head that suddenly fit into place with that one keystone piece: Caesar, then you just keep trying to find some "real Jesus in Palestine." But when most of the "real Jesus in Palestine" has already been lifted away by other research, then finding a real person behind the most significant of the events: the march on Jerusalem followed by the death and resurrection, there really isn't anything left.
But to get there, you have to read and hold in your memory banks, literally hundreds, if not thousands, of books and papers. I see now that my years and years and years of study in comparative religions and Judaism and Christianity in particular, have served me well.
As to Islam, I already covered a goodly part of it in its origins in HoM. I already know the "rest of the story" which will be covered in an upcoming volume.