THE UNICORN LEGEND owes its existence in part to a creative translation in the Septuagint:

The Natural History of Unicorns by Chris Lavers

The Sunday Times review by Rosemary Hill

In this beguiling book, Chris Lavers pursues the unicorn across two and a half millenniums, from the bas-reliefs of ancient Persia to the royal coat of arms of the United Kingdom by way of medieval tapestry. As a scientist, his main purpose is to find out what zoological truths lie behind the myth. But he is also a careful explorer of folklore, sifting fact from fiction.

The first known description of a unicorn comes in 398BC from the Greek doctor Ctesias of Cnidus, who in a book called Indica wrote about “certain wild asses which are as large as horses” and “have a horn on the forehead which is about a foot and a half in length”. This first unicorn was a colourful beast, white with a dark red head, blue eyes and a crimson, white and black horn. Lavers concedes that Ctesias was “a library type of fellow” who had never actually seen what he was describing, but that doesn't mean he was a fantasist. He was right, for example, about elephants, which must have seemed equally implausible to him, and about talking birds (which we now know as parrots).

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More details were added to Ctesias's original picture over time, but for more than six centuries the legend of the beast whose single horn, if you could catch one, had curative properties remained in essence unchanged. The very different creature of later western myth - symbolic, semi-sacred - was born when the unicorn “popped up”, as Lavers puts it, most unexpectedly, in the Greek Old Testament. This beast of savage power, whose name in the Greek is translated from the curious Hebrew word “reem”, rampages through the books of Numbers, Deuteronomy, Job and several Psalms. “The unicorns shall come down with them,” Isaiah warns the enemies of God, “and their land shall be soaked with blood.”

Opinion divided sharply among early scholars as to what this Hebrew word “reem” might have meant. St Jerome in the 4th century was among those who thought it might perfectly well be a rhinoceros, and so it appeared in the Vulgate. To the more metaphysically inclined, though, something less lumbering and more spiritual seemed appropriate. Tertullian of Carthage saw the unicorn as a precursor of Christ that “pierces every race with faith”.

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More on unicorns in the Bible here. And this and this are perhaps relevant as well.