 The English hymnologist James Mearns found it in a manuscript of the British Museum which dates back to about 1370.In the library of Avignon there is preserved a prayer book of Cardinal Pierre de Luxembourg (died 1387), which contains the prayer in practically the same form as we have it today.It has also been found inscribed on one of the gates of the Alcázar of Seville, which dates back to the time of Pedro the Cruel (1350–1369).