Lucian De saltatione 36

[36] Before all else, however, it behoves her to enjoy the favour of Mnemosyne and her daughter Polymnia, and she endeavours to remember everything. Like Calchas in Homer, the dancer must know “what is, and what shall be, and was of old,” ¹ so thoroughly that nothing will escape him, but his memory of it all will be prompt. To be sure, it professes in the main to be a science of imitation and portrayal, of revealing what is in the mind and making intelligible what is obscure. What Thucydides said of Pericles in praising the man would also be the highest possible commendation of a dancer, “to know what is meet and express it;” ² and by expressing I mean the intelligibility of his postures. But his whole accoutrement for the work is ancient story, as I have said, and the prompt recollection and graceful presentation of it.

[36] But above all Mnemosyne, and her daughter Polyhymnia, must be propitiated by an art that would remember all things, Like Calchas in Homer, the pantomime must know all ‘that is, that was, that shall be’; nothing must escape his ever ready memory. Faithfully to represent his subject, adequately to express his own conceptions, to make plain all that might be obscure;—these are the first essentials for the pantomime, to whom no higher compliment could be paid than Thucydides’s tribute to Pericles, who, he says, ‘could not only conceive a wise policy, but render it intelligible to his hearers’; the intelligibility, in the present case, depending on clearness of gesticulation.