Ars Magica

Ars Magica is a medieval fantasy roleplaying game in which magic, legendary creatures, the divine and the infernal all exist. It is also known for otherwise cleaving closely to historical record. Players are typically wizards belonging to the Order of Hermes, or other characters affiliated with the Order.

Links:

Official Site

http://www.atlas-games.com/arsmagica/

Wikipedia

http://en.wikipedia.org/wiki/Ars_Magica

RPG.net Game Index

http://index.rpg.net/display-entry.phtml?mainid=32