Ein' feste Burg ist unser Gott (A mighty fortress is our God) is a chorale cantata by Johann Sebastian Bach (BWV 80). The work had found its present form by 1744 or earlier, but was first performed between 1727 and 1731. Most of the cantatas that Bach composed in Leipzig were intended for Sunday services, but Ein' feste Burg was his contribution to a festival celebrating the Reformation.
