In the book Indica,which describes India, a Greek historian of the 5th century named Ctesias described many fantastical creatures, such as unicorns, manticores and griffins. Indica only survives today in fragments written by Photius,Patriarch of Constantinople.
Concerning the unicorn,he wrote:
In India, there are wild asses as large as horses, or even larger. Thier body is white, their eyes bluish, and they have a horn on their forehead about a cubit in length. The lower part of the horn is quite white, the middle is black, and the upper part, which terminates in a point, is a very flaming red.
Their faces are also reddish, which is sometimes mentioned in reproductions of this description, sometimes not.
It is thought that since Ctesias never traveled to India, and wrote from the accounts of others, that this description may have been based on an Arabian Oryx seen in profile: