Ein' feste Burg ist unser Gott ("A Mighty Fortress Is Our God"), Op.

The full title is Phantasie über den Choral "Ein' feste Burg ist unser Gott".

[6] Ein' feste Burg ist unser Gott, as other chorale fantasias by Reger, is more often performed in concert than in liturgical church services, because of its dimensions.

[5] Reger commented the alleged difficulty of his organ works in 1900 to his friend the organist Gusav Beckmann: "Meine Orgelsachen sind schwer, es gehört ein über die Technik souverän herrschender geistvoller Spieler dazu" (My organ pieces are difficult; they need a skillful player who masters the technique).

[7] The organist Alfred Sittard first recorded this work by Reger on shellac in 1908 on the Sauer organ of the Berlin Garnison Church.