Hesiod, Theogony

There are their bright dancing places and beautiful homes, and beside them the Graces and Himerus （Desire） live [65] in delight. And they, uttering through their lips a lovely voice, sing the laws of all and the goodly ways of the immortals, uttering their lovely voice. Then went they to Olympus, delighting in their sweet voice, with heavenly song, and the dark earth resounded [70] about them as they chanted and a lovely sound rose up beneath their feet as they went to their father. And he was reigning in heaven, himself holding the lightning and glowing thunderbolt, when he had overcome by might his father Cronos; and he distributed fairly to the immortals their portions and declared their privileges. [75] These things, then, the Muses sang who dwell on Olympus, nine daughters begotten by great Zeus, Cleio and Euterpe, Thaleia, Melpomene and Terpsichore, and Erato and Polyhymnia and Urania and Calliope,¹who is the chiefest of them all, [80] for she attends on worshipful princes: whomever of heaven-nourished princes the daughters of great Zeus honor and behold at his birth, they pour sweet dew upon his tongue, and from his lips flow gracious words. All the people [85] look towards him while he settles causes with true judgements: and he, speaking surely, would soon make wise end even of a great quarrel; for therefore are there princes wise in heart, because when the people are being misguided in their assembly, they set right the matter again [90] with ease, persuading them with gentle words. And when he passes through a gathering, they greet him as a god with gentle reverence, and he is conspicuous amongst the assembled: such is the holy gift of the Muses to men. For it is through the Muses and far-shooting Apollo that [95] there are singers and harpers upon the earth; but princes are of Zeus, and happy is he whom the Muses love: sweet flows speech from his mouth. For although a man has sorrow and grief in his newly-troubled soul and lives in dread because his heart is distressed, yet, when a singer, [100] the servant of the Muses, chants the glorious deeds of men of old and the blessed gods who inhabit Olympus, at once he forgets his heaviness and remembers not his sorrows at all; but the gifts of the goddesses soon turn him away from these.