Anyone like Sci-fi and fantasy stories of alternative histories? I looove them.

Ok, if Jesus never existed. My guess.

Judaism would still be a cult among many religions with many gods, they may or may not still be in diaspora. Romans would probably adopt Atheism because their pantheon is just lame, who believes in that nowadays? Rome would probably not exist today.

It would be like Celtic-British Druidism, only the wierdos are druids nowadays. Most of the urbanites would probably eventually be atheist. There would really be no religion to fill in the gap that anyone would accept. Islam would never have existed since Mohammed got his inspiration from both Judaism and Christianity. Christianity focused allot of people's attention to Judaism itself. The curious factor.

Probably lots of human sacrifice, strange witchcraft, and most of the world would still be ignorant, superstitious and living like the tribes in the Amazon.

.... that Buddhism would be the world's largest religion.

not really because the further you get from India, the different the religion gets. If it got far enough it probably would no longer be bhuddist. It would probably be bigger, but im guessing a morphed version reaching COnstantinople, but not really further. Japan is pretty far away, but that is due to the ocean, being easier for trade, in comparison to land routes.

Well, what I meant was, Islam probably wouldn't exist if Jesus hadn't existed, so what's left? As you say, probably Hindu and its derivatives.

As usual with religion, it takes on its own character depending on the location and how isolated it is. For instance Zen derives from the Chinese "Chan", but it has such a different character in Japan that it's almost unrecognizable.

On the other hand, we do have Nichiren sects down here in California, and they're a lot like the ones in Tokyo.

I do suspect that if Jesus hadn't spread the "good news" in the West, that some form of Buddhism would probably have caught on at some point, not the austere kind but probably more along the lines of Mahayana.

Christianity and Buddhism do have a lot in common, philosophically. If you read through the history of the early Christian Church, you'll see why.

Anyone can claim anything about Buddhism.

Buddhism is pure mysticism. Like lame Druidism and Wiccans, innefectual spellcasters who pretend to be important.

Ignoring the ever-so-boring attacks on any religion not Christianity...

Buddhism would likely still dominate the East.
Most likely some Roman or another would begin a monotheistic cult that would catch on to be the "Universal Religion of the Roman Empire" (still called Catholicism).
Alternately, the polytheistic religion of Rome would be translated into either a pantheistic versionin which the gods were just symbols of a real God or dualism where Zeus would be venerated above all and all other gods would be demoted to minor ones under him. Most likely pantheism, inspired by Hinduism.
Either way, such a step would be necessary to begin a moralistic religion to go along with the moralistic philosophies that Greece and Rome were developing. They'd need a religion that could make use of such philosophies and dispose of the superstition-based nature of the old polytheism.

Over time there would be more prophets and messiahs and other bigtime cult-starters. But the likelihood being, since Rome was very big on spreading, that whatever religion Rome professed would be the one to conquer the West.
Despite being pantheistic, the new Roman religion would hold a lot in common with medieval Christianity because it would come out of the same political framework and culture. Various scholars would wind up inspired to write letters and sermons and poetry, which would be selectively compiled into a book. Though unlike with Christianity, there would be no older book to build off of.
Chances are a form of Islam would still have a chance of forming, inspired only by Judaism... Or perhaps, Muhammed would just convert to Judaism and create a zealous version of it rather than a whole new religion.
So the major religions in the world would be:
1)Catholicism (the non-Christian version)
2)Buddhism
3)Hinduism
4)Muhammed-based Judaism
5) Traditional Judaism
Eventually we could expect, based on the philosophical leanings of the Greco-Roman world a kind of split in Catholicism over moralistic issues. Some splits would catch on, others not. Most likely one would adapt especially well to scientific method and economics... but not certain if that would be the same one to get into philosophy about freedom... probably if economics were involved.
The main difference we'd see by the time we get to an era resembling our modern one (which might take more or less time) is that there would probably not be a central figure considered both God and a human in the main Western religion. Most likely salvation would still be tied to faith, as that is part of what would make the most successful cults successful.
Other than that, it's about impossible to speculate on all the weird minor changes that might lead to others. But overall most science and philosophy would be based on the same Greco-Roman stuff.
But what would the calendar look like?

__________________
"It's never over... BOY!"
The Tall Man, Phantasm III

This subject would be the perfect theme for a speculative novel. Imagine all the little things such a difference would make. If a monotheism were formed around the old Roman polytheism with Zeus as God and all others angelic beings, today we'd all be saying Oh My Zeus! and Zeus (*)(*)(*)(*)(*)(*)! Where the Hades are My Keys!

I know java has a lot of knowledge in religious studies, so I'll take his word on the generalities. I've only recently taken an interest studying religions comparatively, although I have just finished an interesting book about Mormonism.

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Aw man.... Righty, I very rarely say this, but in this case, "you are wrong, my friend".

Buddhists are the "engineers" of the spiritual world. If you want to know about "how to", go to a Buddhist.

('Course all Buddhists are not alike, but the ones that are relatively "advanced", let's say, can be pretty mind-boggling).

Generally speaking, they're just about the farthest thing from Druids and Wiccans that there is.

I know I won't be able to convince you of that with a few simple words, and really it's not something you can "learn by reading" anyway - but when you practice and actually "do", you'll realize how deep Buddhism can be.

'Course, we could probably say the same thing about Christianity - just that 99.44% of the Christians out there have no idea what they're talking about, when it comes to spiritual matters. They love to regurgitate the Bible, but when it comes to facility and capability, most of 'em are sadly lacking. They're "drunk on cheap wine", as the Gospel of Thomas infers, and they have yet to taste the Chateauneuf du Pape.

It's all good. Some spirituality is definitely better than none.

Do you know anything about Bhuddism?

I know how to spell Buddhism.
Probably not any more than you do. I understand the very basics of Buddha's teachings, I understand that there is significant variety in Buddhism, and all the crap everyone knows. Stekim's the resident Buddhist.
I'm more interested in the anthropology of religion than the content of any given religion.
Studying religion on broad terms, you figure out that religion is a lot like language: The words are only a small part of the whole... but there's always the @$$hole that wants to correct every little word to its 19th century correctness. It is also mostly symbols to communicate something and it changes fast and within very few generations in isolation you get a new one.

The way I see it the reasons Buddhism spread parellel the reasons Christianity spread, while Hinduism and Judaism both represent older religions that survived the new ones and adapted slightly to keep up with the times.
Looking at Islam's founding, you see one of the things going on here. Muhammed was shocked that the Jews and Christians didn't jump on board with Islam. Instead he converted a lot of pagans.
Similarly Christianity replaced pagan religions in the Roman empire, but was only a small cult movement within Judaism. And Buddhism spread throughout Asia displacing their pagan religions or integrating with them, while becoming virtually nonexistent in India where it was born.
The reason? These religions had plenty to offer the pagans, but little to offer their parent religions.

That's why regardless of whether Christianity was born out of Judaism, we'd still be very likely to see new religions form as regional super-religions rather than continuation of pagan religions. Pagan religions work well for people before science progresses when it seems that most of life is outside of human hands. Buddhism, Christianity, and Islam do more to place the world into human hands by making human action more important. They use the moralistic basis from the evolved forms of Judaism and Hinduism, something lacking from the pagan religions.
Over time, you'll see. Religions that don't keep up with the progress of a civilization or offer its people hope die off. Either that or they adapt. And failing that, someone has a revelation and a new religion or sect pops up.

__________________
"It's never over... BOY!"
The Tall Man, Phantasm III