The precise composition date of 'Ein feste Burg ist unser Gott' is disputed. Luther's Wittenberg colleague Justus Jonas placed it in 1527 — the year the bubonic plague reached Wittenberg and Luther refused to flee, treating the sick in his own house at the Black Cloister while his wife Katharina was pregnant with their second child.
The text is a loose paraphrase of Psalm 46 ("God is our refuge and strength") in four stanzas, first published in Andreas Rauscher's Erfurt hymnal of 1531 (the 1529 edition sometimes claimed as the first print is lost). Luther wrote both the text and the melody — one of the few tunes indisputably his — and it appeared in his own 1533 Klug'sche Gesangbuch.
"The Diet of Augsburg (1530), the Diet of Speyer (1544), and every Lutheran military engagement of the Thirty Years' War (1618–1648) was accompanied by the singing of the hymn — Gustavus Adolphus of Sweden reportedly had it played before the Battle of Breitenfeld (1631) and before his own death at Lützen (1632)."
Frederick the Great called it "God Almighty's grenadier march". Heinrich Heine, an unbeliever, described it as "the Marseillaise of the Reformation". J.S. Bach used it as the basis for Cantata BWV 80. Mendelssohn quoted it in the finale of his 'Reformation' Symphony (1830). Meyerbeer used it as the leitmotif of the Huguenot opera.
Luther himself asked for it at his deathbed in Eisleben on 18 February 1546. He died reciting the first line.