Weihenstephan
The bavarian Staatsbrauerei Weihenstephan, founded in the year 1040, is the oldest still existing brewery of the world. While it is really really old it might not be that old. The brewery was originally part of the benedictine monastery Weihenstephan. The document from 1040 is most probably a fake abbot Georg Tanner got made made about 600 years later.
Anyway, their beer is quite good.