Thus these Sequences have become verse before our eyes, and we realize that it is the very central current of the evolution of mediaeval Latin poetry that we have been following. How free and how spontaneous was this evolution of the Sequence. It was the child of the Christian Middle Ages, seeing the light in the closing years of the ninth century, but requiring a long period of growth before it reached the glory of its climacteric. It was born of musical chanting, and it grew as song, never unsung or conceived of as severable from its melody. Only as it attained its perfected strophic forms, it necessarily made use of trochaic and other rhythms which long before had changed from quantity to accent and so had passed on into the verse-making habitudes of the Middle Ages.[311] If there be any Latin composition in virtue of origin and growth absolutely un-antique, it is the mediaeval Sequence, which in its final forms is so glorious a representative of the mediaeval Hymn. And we shall also see that much popular Latin poetry, “Carmina Burana” and student-songs, were composed in verses and often sung to tunes taken--or parodied--from the Sequence-hymns of the Liturgy. There were many ways of chanting Sequences. The musical phrases of the melodies usually were repeated once, except at the beginning and the close; and the Sequence would be rendered by a double choir singing antiphonally. Ordinarily the words responded to the repetition of the musical phrases with a parallelism of their own. The lines (after the first) varied in length by pairs, the second and third lines having the same number of syllables, the fourth and fifth likewise equal to each other, but differing in length from the second and third; and so on through the Sequence, until the last line, which commonly stood alone and differed in length from the preceding pairs. The Sequence called “Nostra tuba” is a good example. Probably it was composed by Notker, and in his later years; for it is filled with assonances, and exhibits a regular parallelism of structure. “Nostra tuba Regatur fortissime Dei dextra et preces audiat Aura placatissima et serena; ita enim nostra Laus erit accepta, voce si quod canimus, canat pariter et pura conscientia. Et, ut haec possimus, omnes divina nobis semper flagitemus adesse auxilia. * * * * * O bone Rex, pie, juste, misericors, qui es via et janua, Portas regni, quaesumus, nobis reseres, dimittasque facinora Ut laudemus nomen nunc tuum atque per cuncta saecula.”[312]