Cassiodorus, who lived still in 562, aged almost 100 years, left a souvenir for music in the fifth chapter of his treatise on the "Discipline of Letters and Liberal Arts" (_De Artibus ac Disciplinis Litterarum_). He enumerates the fifteen modes of Alypius as not having been abandoned, and establishes them in their natural order, calling them tones. Here also we find the classification of six kinds of symphonies, about 300 years after this enumeration, first realized in notes by Hucbald. He gives a series of fourths and of fifths, occasionally for two voices, occasionally with the octave added. These are the most important of all the things concerning music to be found in that part of Cassiodorus' book dedicated to music. In the seventh century the first, or perhaps the only author who wrote upon music was Bishop Isidore, of Seville. In his celebrated treatise on the etymologies or origins ("_Isidori Hispaniensis Episcopi Etymologiarum, Libri XX_") divided into twenty books, chapters XIV to XXII of the third book relate to music. These are the chapters published by the Abbe Gerbert, under the name of "_Sentences de Musique_," in the collection of ecclesiastical writers upon this art, after a manuscript in the imperial library at Vienna. While many of these chapters contain nothing more than generalities and pseudo historical anecdotes concerning the inventors of this art, this is not the case with the nineteenth chapter, the sixth in Gerbert's edition, for here he speaks "Of the First Division of Music, called Harmony." The definitions given by St. Isidore have a precision, a clearness not found in other writers of the Middle Ages. "Harmonic music," says he, "is at the same time modulation of the voice, and concordance of many simultaneous sounds. Symphony is the order established between concordant sounds, low and high, produced by the voice, the breath or by percussion. Concordant sounds, the highest and the lowest, agree in such way that if one of them happens to dissonate it offends the ear. The contrary is the case in diaphony, which is the union of dissonant sounds." Here we find St. Isidore employing the term diaphony in its original sense, as a Greek word, meaning dissonance--a sense exactly opposite to that of Jean de Muris. The Venerable Bede was the light of the eighth century, and the glory of the Anglo-Saxons. His treatise upon music, however, deals in theories and generalities, throwing no light upon the music of his day. The elevation of his ideas may be seen in the following sentence, with which he introduces his subject: "It is to be remarked that all art is contained in reason; and so it is that music consists and develops itself in relations of numbers." ("_Notandum est, quod omnis ars in ratione continetur. Musica quoque in ratione numerorum consistit atque versatur._")