Lucian of Samosata De saltatione 19

[19] Since we have spoken of India and of Ethiopia, it will repay us to make an imaginary descent into Egypt, their neighbour. For it seems to me that the ancient myth about Proteus the Egyptian means nothing else than that he was a dancer, an imitative fellow, able to shape himself and change himself into anything, so that he could imitate even the liquidity of water and the sharpness of fire in the liveliness of his movement; yes, the fierceness of a lion, the rage of a leopard, the quivering of a tree, and in a word whatever he wished. Mythology, however, on taking it over, described his nature in terms more paradoxical, as if he became what he imitated. Now just that thing is characteristic of the dancers to-day, who certainly may be seen changing swiftly at the cue and imitating Proteus himself. And we must suppose that in Empusa, who changes into countless forms, some such person has been handed down by mythology. ¹