In the year 860, Norsemen sacked the cloister of Jumièges in Normandy, and a fleeing brother carried his precious Antiphonary far away to the safe retreat of St. Gall. There a young monk named Notker, poring over its contents, perceived that words had been written in the place of the repetitions of the final _a_ of the Alleluia. Taking the cue, he set to work to compose more fitting words to correspond with the notes to which this final _a_ was sung. So these lines of euphonious and fitting words appear to have had their beginning in Notker’s scanning of that fugitive Antiphonary, and his devising labour. Their primary purpose was a musical one; for they were a device--mnemotechnic, if one will--to facilitate the chanting of cadences previously vocalized with difficulty through the singing of one simple vowel sound. Notker showed his work to his master, Iso, who rejoiced at what his gifted pupil had accomplished, and spurred him on by pointing out that in his composition one syllable was still sometimes repeated or drawn out through several successive notes. One syllable to each note was the principle which Notker now set himself to realize; and he succeeded. He composed some fifty Sequences. In his work, as well as in that of others after him, the device of words began to modify and develop the melodies themselves. Sometimes Notker adapted his verbal compositions to those cadences or melodies to which the Alleluia had long been sung; sometimes he composed both melody and words; or, again, he took a current melody, sacred or secular, to which the Alleluia never had been sung, and composed words for it, to be chanted as a Sequence. In these borrowed melodies, as well as in those composed by Notker, the musical periods were more developed than in the Alleluia cadences. Thus the musical growth of the Sequences was promoted by the use of sonorous words, while the improved melodies in turn drew the words on to a more perfect rhythmic ordering. Notker died in 912. His Sequences were prose, yet with a certain parallelism in their construction; and, even with Notker in his later years, the words began to take on assonances, chiefly in the vowel sound of _a_. Thereafter the melodies, seizing upon the words, as it were, by the principle of their syllabic correspondence to the notation, moulded them to rhythm of movement and regularity of line; while conversely with the better ordering of the words for singing, the melodies in turn made gain and progress, and then again reacted on the words, until after two centuries there emerged the finished verses of an Adam of St. Victor.