More reflections on religion in fantasy worlds

Lately I've been working on a new story. It's fantasy, but set in a sort of alternate-history version of the real world, so I don't have to do as much world building as if I was starting from scratch. For example, the geography is the same, aside from the location of borders and man-made features such as canals. But the historical change is big enough that I can't just use real-world governments or religions.

All this got me thinking about fictional religions again. In spite of the obvious influence of real-world religions on fiction, I can't think of a fantasy world that simply uses a real religion. In fact, though the writers are often Christian, or at least live in largely Christian societies like the United States, and although the model for a lot of fantasy is medieval Europe, fantasy religions are often polytheistic. Perhaps this is because fantasy religions are taken to be true for the world in which they are set, with gods whose clerics possess real powers, which might be less plausible if it was a real religion that we knew about. I think the nostalgia some people have for the polytheistic faiths of Europe that were replaced or subsumed by Christianity also plays a role.

Urban fantasy, of course, uses real religions for the most part, but what I'm mostly interested in is fantasy set on a different world or a very different version of this one.

So how do writers create religions, from a psychological point of view? In my case, the story I'm working on takes Gaulish beliefs, about which we know very little, as a jumping-off point. I've created a national myth, a sort of collective origin story, for the culture from which the main character comes, a story that explains why many in that society exhibit magic powers. From there, I'm trying to work out how that would affect religious belief and practice, and how other societies would react to my characters and their powers. I'm finding that it takes a lot of work to dream up a culture, even starting from something that really existed.

But I still have to wonder. Does the creation of a fictional religion parallel in any way the creation of a real-life new religious movement? I mean, I suspect most religious leaders are in earnest, but even so, do the same tendencies come out in fiction as in religious belief? The same ideas about what is and is not religion, about what kind of truth-claims one can credibly make? I suppose these questions are as much sociological as psychological, and they are rather beyond the scope of this blog.