I like this. Would make obvious why magi live in strong auras. I would make it Aura strenght +2, though, so an aura 3 allows level 25 spells, and aura 0 level 10 spells. Aura 5 would be enough for 7th magnitude, but you need strong auras to cast the large rituals. Quite something there! Might have to steal part of it 
Cheers,
Xavi
Steal all you want, a lvl 0 aura is very rare in our system, and worth investigating in its own right. There are also higly mutable aura's
Well, in this specific case, you could argue that medieval Europe was almost entirely Christian and certainly very Eurocentric, so depicting it as such is historical reality, not cultural imperialism. I believe that Atlas Games did have vague plan to extend the setting past Europe, but so far it hasn't happened.
That said there is very little that needs doing to change it as far as the rules are concerned. Make the Limit of the Divine a Lesser rather than Greater Limit: basically, Hermetic Magic cannot affect the Divine because deep down Hermetic Mages believe it can't; other traditions might not even notice. The same for the Limit of Essential Nature, since it is the product of Greek philosophy. Fudge the rules on aura interactions a little to remove all references to the Divine being privileged. That means Hermetic Magic remains the product of a Christian Europe, but that's where this tradition was created; you'll have to create alternate traditions for alternate beliefs yourself.
Of course, you still have the Divine and Infernal as specific, separate Realms, but that's only because most people believe in them in Europe. Magic and specially Faerie lump together most pagan religions, but that's because those religions tend to be compatible with each other and recognize each other's gods as actual gods (and those gods are in fact extremely powerful Faerie, or more rarely Magic, beings; and the Divine is the Divine because monotheist religions accept that they all worship the same god by a different name, although of course those filthy heretics next door have got their worship all wrong; and the Divine is separate from Faerie because the one true god doesn't recognize those pagan gods as gods at all). Possibly if enough people believe in a different set of gods that do not accept foreign gods as even valid, they could create a new Realm. And there would be no Dominion or Infernal Aura anywhere in 13th century America or Australia, and in large areas or Asia and Africa, because those places were never exposed to those beliefs.
The Cradle and the Crescent?
I don't have the book, but while the Levant isn't in Europe, the Crusader realms are very much culturally part of Europe... And even the Muslim world is still very much influenced by a monotheistic religion and greco-roman philosophy.
C&C is about what surrounds the crusader states more than the crusader states per se. But yes, it is still based on the world map. The game is eurocentric after all, as medieval Europeans (and current Europeans) view themselves. It is a game design decision.
Simply make the changes your require to the "trump" value of the Divine, and voila. The systems for Divine/Fairy/Magic/Demonic are all nearly identical and you can include/exclude/shift around any myths between the 4 areas. Just don't delve too deeply into the "spread" of dominion or how the Magi simply havent ruled all since you probably won't have divine lightning-bolts or blindness to keep Hubris in check.
You'll still be just as culturally imperialistic as the base game though, but your culture is simply Gray-Egalitarianism .
Also note that it's not actually Mideval Christianity that AM is being close to. Of the monotheistic religions, the underlying metaphysics is actually closer to Islam than Christianity or Judiasm. (Islam acknoledges the existence and partial validity of the other two religions as "people of the book" - Moses and Jesus are considered prophets in Islam. In contrast, Christianity tends to look as Judiasm as "Ooh, so close and yet so far" and Islam as "Um, no." I think Judiasm just kind of looks at the other two, rolls it's eyes while saying "oy, vey", and walks away.) But even that AM interpetation of the Divine only works if you don't look at it too closely, or else paper over it with "The Divine works in mysterious ways".
EDIT - I suppose you can kind-of get away with (of all things) applying a hindu-esque "facets of the Divine"/"there are many paths to God" idea - which makes sense if you think of Hinduism as a conglomeration of a bunch of different religions that over time interwove their own theologies together...
You misunderstood me, I actually meant the rest of the world like Asia, Africa, Middle East, Americas, Australia, etc where defining them via a Euro/christian centric view (for example which first of all defining the rest of the lands outside of Europe as the "magical lands of Cathay or the Holy Kingdom of Prester John" and also defining other religions/culture's Deities as primarily either Angels/Saints or Demons or secondarily as Faeries or even just "Dreams created humanity" therefore Abrahamicism rising above all the other religions/mythologies which for example Supernatural's "Hammer of the Gods", the way In Nomine treats other gods, etc) and of course exorcizing those cultures (for example the Kuie-Jinn from Kindred of the East from White Wolf's World of Darkness fame) is a example of cultural imperialism (As in "The West is right and the rest of the world is wrong" just because the west is currently dominate).
In short: Ever noticed that most western developers keep falling the same trap of Eurocentricism which is apparent in western media which for example this explains it better here.
I hope your not suggesting one religion/mythology to rise above all the others by suggesting that all religions lead to the Abrahamic God therefore "Abrahamicism is the only truth".
Well what I also meant is Crossover Cosmology as well which was I was suggesting all along.
I think, that you can make yourself far better understood here by picking one of the very few representations of non-abrahamic cultures from Ars Magica 5 supplements - like the Soqotrans from Rival Magic, or the Zoroastrians from The Cradle &The Crescent - and explaining at that example what you like about it and what you dislike, how it is eurocentric and how it should be instead.
Cheers
What Ars tries to describe is a believable environment wher magi could exist, it is almost entirely set in europe, because that is a type of myth that has some internal logic to it. It tries to emulate beliefs and paradigm that link to the european minds of the time. Take it further from europe and the medieval european worldview would crumble, as would the rules of Ars if you don't adjust them. Take it back in time and it would crumble as well, because the dominion is of lesser importance. You seem to have issue that Ars is christian and eurocentric. The issue is that european paradigm is christian and eurocentric, it is a few hundred years late to change that.
Well thing is, the medieval European paradigm should only work in medieval Europe and stay in Europe while the rest of the world has completely different paradigms (For example in Asia Hinduism/Buddhism/Taoism/Jainism/etc are true).
Of course another conflict is European pre-christian religions as well since Europe can't be all Christian.
So truth should depend on geographic location in your games? When Frate Giovanni da Pian del Carpine 1245-1247 pursued his mission to meet and convert the Great Khan into the Karakorum, by his report he didn't notice any 'paradigm changes', but certainly many cultural differences on his way. To keep the game viable, I would expect that people from different cultures in the same game world, just like real people, bring to a very high degree their own paradigms with them where they go - and the rules and SGs have to cover that gracefully, without detailing lots of cosmologies.
Cheers
I think a better idea is to have paradigms overlapping each other based on culture or something (well except how can we keep one from rising above another and have them equal power?). Well any idea how can the 'truth' be presented equally or maybe there is no "Truth/False" dichotomy....
Of course another question which for example how can we have the Lands of Cathy/Holy Kingdom of Prester John and the actual lands (China and Africa) both exist and equally being true at the same time without violently conflicting each other?
Well actually I just found a list of mythical locations:
en.wikipedia.org/wiki/List_of_my ... cal_places
Maybe the world during the past used to be endless possibilities until the modern world solidified it into a planet when the Technocratic paradigm came to dominate which the previous paradigms became just left overs from the past.
This usually requires only a discrete SG, who knows the paradigms by which the characters see the world and act in it. I don't see any market for rules about resolving conflicts of cosmologies described in great detail. (TORG tried it on a more abstract level, made conflict of cosmologies its main game theme - and is no longer around. There may be a reason for it.)
Given that the reports about Prester John's lands and his letter are philologically traceable fakes, there is no reason to have a kingdom of Prester John anywhere at all: nobody's 'cosmology' or 'paradigm' suffers. After all, Giovanni da Pian del Carpine and Wilhelm von Rubruk did look for it and reported back how they could not find it, but heard some stories. If some faerie or spirit wants to play Prester John, it is of course welcome as well, and need not stick to Otto von Freising and the 'Chronica sive Historia de duabus civitatibus' slavishly.
That's a game for you to write, if you care.
Cheers
No, I don't... because I've seen games that don't do that. Ars Magica isn't one of them, because Ars Magica is very specific and focused in it's setting... Mythic Europe. I see no need to apologize for that. If you're looking for a game that's about magic in Ancient China, or you want to roleplay in a fantasy version of Mayan America or medieval Japan... there are probably games for that. Ars Magica isn't that game.
I suppose you could design a game which tried to cover all the various mythological paradigms as separate but adjacent realms. Assuming the game designers head's didn't explode, I think you'd either end of with a very superficial and cliche treatment of each of the represented cultures, simply because there is far too much to deal with in any depth.
First, there are political, real-world, reasons to have a Dominion represent the One True God. Some people cannot accept that their beliefs are but beliefs. Since the Spaghetti Monster is not falsifiable, if He was to bless us with His Noodly Appendanges I would consider him a Faerie and not change my beliefs. If there was a Second Coming, who would update their beliefs, who would denie it as Faeries/Devil, and who would be right?
Second, in the same way that ice is solidified water, the Dominion could be construed to be a solidified Faerie aura when everyone believes the same. That might be enough to nullify euro-centrism.
That leaves Prester John in a hidden valley, or a humongous Regio. Maybe there are dinosaurs and mammouth too.
Well do you know any games that your speaking of?
Of course the bolded part was what I was suggesting all along (do any games like this already exist by any chance? I originally thought Ars Magica was one of them which unfortunately I was mistaken) and if game developers took their time to research into those cultures or even have people from Asia/Africa/etc help them or even write them I don't think it would be that hard if they put effort to it.
I'm pretty sure GURPS has sourcebooks for a lot of that. Alas, I don't remember any specific games though having seen the variety of stuff at GenCon and talking a number of diverse gaming friends, I'm sure they are out there. Honestly I never paid much attention because I'm not that interested in them.
Think about how many different sourcebooks Ars Magica has just dedicated to Mythic Europe and those gloss over the diversity of local mythology and folklore found just in Europe. Asia, Africa, Ancient Amercia... all are home to a wide array of cultures, folklores and traditions. To do it right, I think you would need to do something like Rifts or World of Darkness, where you have separate but compatible games in a shared multi-verse. I don't know any game like that, not that sticks to historical folklore. It would be an ambitious project... but not one I would have any interest in as a consumer.
Bushido, Legend of the Five Rings, Tekumel, WoD's Kindred of East, D&D's Oriental Adventures are all Asian orientated (see what I did there!) role-playing products.
ArM is set in a particular place, Mythic Europe. In that context it makes little sense to talk in detail about other places.
If you want a game about the Mayan or Japanese Empires you are much better off with a game set specifically in those places.