Bach J.S. - Cantata No. 80: Ein feste Burg (BWV 80) (Urtext).

There are practically no surviving original sources for Bach's great Reformation Cantata "Ein feste Burg ist unser Gott". It is possible that the original form of the Cantata was written in Weimar in 1715 to which Bach later made various additions and alterations to transform it into a Reformation Cantata for Leipzig.

Although scholarly opinion as to the sources is divided there is no doubt that the opening chorus, based on Martin Luther's chorale melody "Ein feste Burg" is one of Bach's greatest achievements.