There is(was) a LARP in Montreal called Terres d'Aragon (Aragorn's land). It is based on the battle between three(and more) religions:

The Avalons are King Arthur's army consisting of its mages, soldiers (fighters) and priests. It is the major religion in Terres d'Aragon and is also one of the strongest (or perhaps, The strongest). Some characters that I remember were Bartur, Furegore and of course, King Arthur. Their colour was Red.

Odinic (Odinique from the God, Odin)
The Odinics (or the Anglo-Saxons) were supposedly barbarians, but if you ask me we were more like Goths (which is funny considering the Romans called barbarians, Goths, but I'm talking about today-Goths). Anyways, the Odinics were organized in a hierarchial style IIRC: bosses (these were from various classes) -> mages -> thieves -> fighters. Not consistently like this however. Odinics were also (supposedly) the evil dudes. Their colour was Black.

Christians were supposedly the peaceful religion. They were dominated by Priests, but also had fighters (crusaders). They were probably the fewest and one of the weakest religions. Their colour was yellow.

There are more religions, but the above were the dominating ones. Some others were Myrcule, Gaia and Satanists.

The rules were quite simple. For fighters, if you had a weapon held with one hand, it hit 1 of damage. If you had a weapon that was held with two hands, it hit 2 of damage. But the used sword must be respectively used by one or two hands. You would not use a long sword with two hands. That's just cheating. Then if there was a handy Priest that could empower your sword, it may hit additional damage (like +1 or +2).

Then there was backstabbing, if you backstabbed with any weapon, it'd hit double its normal damage. Thieves had additional damage I believe, as they raised levels.

Mages and Priests had various spells (I do not know as I've never been a Priest or a Mage), but you had to memorize certain spells and throw white powder (starch) at people. Some spells were sleep, paralyze or call monster.

Gaining levels. This was based on how many times you'd go to LARP (a marketing strategy perhaps). As you gained levels, your hit points increased.

Armor class changed with the number of Armoring objects you had. This was determined by an official in LARP. Some examples are Leather Armor, shields or chain mails.

Terres d'Aragon was in Montreal-Nord. I don't really remember where it was exactly, but it was near Pointes-Aux-Trembles (ok, I know I'm not helping, but whatev. Just go ask somebody! I don't know if it still exists though.). It was really fun, costed about $20 CA for a night and we'd go at about 8 till 1 in the morning or later. There'd be battles between the religions, battles against goblins and sometimes you'd just sit there watching dramatic scenes/fights between two dudes. It was in an abandoned house (la maison des jeunes).