Ars Magica is a role-playing game set in 'Mythic Europe' – a historically grounded version of Europe and the Levant around AD 1200, with the added conceit that conceptions of the world prevalent in folklore and institutions of the High Middle Ages are factual reality (a situation known informally as the "medieval paradigm"). The players' involvement revolves around an organization of magi and their allies and foes both mundane and supernatural. The game was originally developed by Jonathan Tweet and Mark Rein-Hagen, with its first edition published in 1987.
https://en.wikipedia.org/wiki/Ars_Magica