Hi!
I found a site that purports to be about Mari people beliefs/religion/mythology (it links to Wikipedia), incase anyone's interested in turning it into a mod Nation at some point, or just learning something new:
Here's the site below, in Russian:
http://virginia.ru/mari-mythology/
Ich's post below this one has a pretty useable version in English.
It's definitely worth checking out.
Here's a wikipedia article on the Mari:
http://en.wikipedia.org/wiki/Mari_people
Apparently they're Volga-Finnic in origin, and considered the first people to live along the Volga river, so not only Russians but Finns on the boards (as well as clueless American history buffs like me
) might find them interesting.