Cicero, On the Republic
2.43.69 (tr. Clinton W. Keyes):
For just as in the music of harps and flutes or in the voices of singers a certain harmony of the different tones must be preserved, the interruption or violation of which is intolerable to trained ears, and as this perfect agreement and harmony is produced by the proportionate blending of unlike tones, so also is a State made harmonious by agreement among dissimilar elements, brought about by a fair and reasonable blending together of the upper, middle, and lower classes, just as if they were musical tones. What the musicians call harmony in song is concord in a State, the strongest and best bond of permanent union in any commonwealth; and such concord can never be brought about without the aid of justice.
ut enim in fidibus aut tibiis atque ut in cantu ipso ac vocibus concentus est quidam tenendus ex distinctis sonis, quem inmutatum aut discrepantem aures eruditae ferre non possunt, isque concentus ex dissimillimarum vocum moderatione concors tamen efficitur et congruens, sic ex summis et infimis et mediis interiectis ordinibus ut sonis moderata ratione civitas consensu dissimillimorum concinit; et quae harmonia a musicis dicitur in cantu, ea est in civitate concordia, artissimum atque optimum omni in re publica vinculum incolumitatis, eaque sine iustitia nullo pacto esse potest.
"[A] Ciceronian period which is itself a picture of the balance and the harmony of
the world," according to Leo Spitzer, Traditio
2 (1944) 423.