found: Grove music online, viewed May 28, 2014(Sequence (i); A category of medieval Latin chant (also called Prosa or 'prose') which flourished from about 850 to 1150. Throughout that period both its musical and literary importance were great; and from about 850 to 1000, when the large repertories were firmly established, the sequence represented one of the most important kinds of music produced in the West-- important because of its intrinsic musical values as well as its historical significance for the development of style in general... Since the sequence itself underwent profound structural modifications in its development, it is not possible to give a simple definition of its form that holds for the entire period; with that reservation, the sequence can be described as a piece of sacred chant of ample dimensions, in length as well as melodic range, set syllabically with a Latin text. The text consisted mostly of a series of couplets each having two isosyllabic lines sung to the same melody; each couplet was different from the preceding couplet in melody and usually in length. In earlier sequences the text was not governed by regular accent patterns or by end-rhyme, hence was indeed 'prose'. After 1000 the texts scanned and rhymed to an increasing degree, finally becoming verse...The texts were often associated with a particular season, feast or saint's day, hence were 'proper' in the liturgical sense. Certainly by the end of the 10th century - and probably by the end of the 9th - they came to be sung at Mass, immediately after the alleluia, as a medieval addition to the Proper of the Mass. In this and in other ways the sequence is related to the alleluia, but the relationship is neither clear nor simple, and has been the subject of controversy.)
