"In playing the lyre or the flute, and of course in choral singing, a degree of harmony has to be maintained among the different sounds, and if it's altered or discordant a trained ear can't stand it; and this harmony, through the regulation of very different voices, is made pleasing and concordant. So too the State, through the reasoned balance of the highest and the lowest orders, is harmonious in the Concord of very different people. What musicians call harmony with regard to song is Concord in the State, the tightest and best bond of safety in every Republic; and that Concord can never exist without justice."
-Cicero, On the Commonwealth