It is said of the three-legged ass that it stands in the middle of the wild sea, and it has three feet, six eyes, nine mouths, two ears and one horn. Its body is white, it eats spiritual food and is virtuous. And two of its six eyes are in the eyes’ place, two on the top of its head and two on it’s rear; with these six sharp eyes it sees all who do evil and destroy.
Of the nine mouths, three are in the head, three on the back and three on the inner side of the flanks, and each mouth is the size of a house. The animal itself is as big as the mountain called Alvand. Each of its three feet take up as much ground as a herd of a thousand sheep when they are gathered together, and each rear part is of such an extent that a thousand men with a thousand horses can be placed within it … The single horn is of gold and hollow, and a thousand branches grow out of it … With that horn it can strike and shatter all corruption that comes from harmful animals.
When that ass submerges its neck in the ocean its ears will terrify, and all the water in the wild sea will tremble with agitation … When it utters a roar, all the she creatures of the sea and Ahura Mazda’s animals will team with young, and all the venomous water creatures will drop their young at that scream. When it makes water in the sea all the water in the seven regions of the earth will be cleansed … And the words say: If thou, O three legged ass, had not been created for the water, all the water in the sea would be corrupted by the infection which the Evil Spirit brought down into its waters on the death of Ahura Mazda’s creatures.
From Persian Zoroastrian writings, The Avesta, trans. L Gotfredsen, quoted in The Natural History of the Unicorn, by Chris Lavers.