Medieval knowledge of the fabulous beast stemmed from biblical and ancient sources, and the creature was variously represented as a kind of wild ass, goat or horse. As in numerous places bible the unicorn appears, it is again associated with qualities like strength, faith, joyfulness and unfalteringness.
Will the unicorn be willing to serve thee, or abide by thy crib? Canst thou bind the unicorn with band in the furrow? or will he harrow the valleys after thee? Wilt thou trust him, because his strength is great? or wilt thou leave thy labour to him? Wilt thou believe him, that he will bring home thy seed, and gather it into thy barn?
He maketh them also to skip like a calf; Lebanon and Sirion like a young unicorn.
...he hath as it were the strength of a unicorn
Unicorns are not found in Greek mythology, but rather in accounts of natural history, for Greek writers of natural history were convinced of the reality of the unicorn, which they located in India, a distant and fabulous realm for them. The earliest description is from Ctesias who described them as wild asses, fleet of foot, having a horn a cubit and a half in length and colored white, red and black. Aristotle must be following Ctesias when he mentions two one-horned animals, the oryx (a kind of antelope) and the so-called "Indian ass". Strabo says that in the Caucasus there were one-horned horses with stag-like heads.
In the persian culture, on the other hand, there is an mythological creature called the Shadhavar. This is – as far as I could find out – the only appearance of an unicornlike creature which is connected to evil characteristics.
Pliny the Elder mentions the oryx and an Indian ox (perhaps a rhinoceros) as one-horned beasts, as well as "a very fierce animal called the monoceros which has the head of the stag, the feet of the elephant, and the tail of the boar, while the rest of the body is like that of the horse; it makes a deep lowing noise, and has a single black horn, which projects from the middle of its forehead, two cubits in length."
Though the qilin, a creature in Chinese mythology, is sometimes called "the Chinese unicorn", it is a hybrid animal that looks less unicorn than chimera, with the body of a deer, the head of a lion, green scales and a long forwardly-curved horn. The Japaneseẻ Ly of Vietnamese myth, similarly sometimes mistranslated "unicorn" is a symbol of wealth and prosperity that made its first appearance during the Duong Dynasty, about 600 CE, to Emperor Duong Cao To, after a military victory which resulted in his conquest of Tây Nguyên. version (kirin) more closely resembles the Western unicorn, even though it is based on the Chinese qilin.
The predecessor of the medieval bestiary, compiled in Late Antiquity and known as Physiologus, popularized an elaborate allegory in which a unicorn, trapped by a maiden (representing the Virgin Mary), stood for the Incarnation. As soon as the unicorn sees her, it lays its head on her lap and falls asleep. This became a basic emblematic tag that underlies medieval notions of the unicorn, justifying its appearance in every form of religious art. The two major interpretations of the unicorn symbol hinge on pagan and Catholic symbolism.
The pagan interpretation focuses on the medieval lore of beguiled lovers, whereas some Catholic writings interpret the unicorn and its death as the Passion of Christ. The unicorn has long been identified as a symbol of Christ by Catholic writers, allowing the traditionally pagan symbolism of the unicorn to become acceptable within religious doctrine. The original myths refer to a beast with one horn that can only be tamed by a virgin maiden; subsequently, some Catholic scholars translated this into an allegory for Christ's relationship with the Virgin Mary. Interestingly enough, the collective term for a grouping of unicorns is called a "blessing of unicorns".
The unicorn also figured in courtly terms: for some 13th century French authors such as Thibaut of Champagne and Richard de Fournival, the lover is attracted to his lady as the unicorn is to the virgin. With the rise of humanism, the unicorn also acquired more orthodox secular meanings, emblematic of chaste love and faithful marriage. It plays this role in Petrarch's Triumph of Chastity.
The royal throne of Denmark was made of "unicorn horns". The same material was used for ceremonial cups because the unicorn's horn continued to be believed to neutralize poison, following classical authors.
The unicorn, tamable only by a virgin woman, was well established in medieval lore by the time Marco Polo described them as: scarcely smaller than elephants. They have the hair of a buffalo and feet like an elephant's. They have a single large black horn in the middle of the forehead... They have a head like a wild boar's… They spend their time by preference wallowing in mud and slime. They are very ugly brutes to look at. They are not at all such as we describe them when we relate that they let themselves be captured by virgins, but clean contrary to our notions. To us, now in 21st century, it is clear that Marco Polo was describing a rhinoceros. In German, since the 16th century, Einhorn ("one-horn") has become a descriptor of the various species of rhinoceros.
The ancient Norwegians were said to believe the narwhal to have affirmed the existence of the unicorn. The unicorn horn was believed to stem from the narwhal tooth, which grows outward and projects from its upper jaw.
In one of his notebooks Leonardo da Vinci wrote: "The unicorn, through its intemperance and not knowing how to control itself, for the love it bears to fair maidens forgets its ferocity and wildness; and laying aside all fear it will go up to a seated damsel and go to sleep in her lap, and thus the hunters take it."
Among numerous finds of prehistoric bones found at Einhornhöhle (Unicorn Cave) in Germany's Harz Mountains, some were selected and reconstructed by the mayor of Magdeburg, Otto Von Guericke, as a unicorn in 1663. Guericke's so-called unicorn had only two legs, and was constructed from fossil bones of a Woolly rhinoceros and a mammoth, with the horn of a narwhal. The skeleton was examined by Gottfried Leibniz, who had previously doubted the existence of the unicorn, but was convinced by it. Baron Georges Cuvier maintained that as the unicorn was cloven-hoofed it must therefore have a cloven skull (making the growth of a single horn impossible); to disprove this, Dr. W. Franklin Dove, a University of Maine professor, artificially fused the horn buds of a calf together, creating a one-horned bull.
Since the rhinoceros is the only known extant land animal to possess a single horn, it has often been supposed that the unicorn legend originated from encounters between Europeans and rhinoceroses. The Woolly Rhinoceros would have been quite familiar to ice age people, or the legend may have been based on the rhinoceroses of Africa. Europeans and West Asians have visited Sub-Saharan Africa for as long as we have records.
However, according to the Nordisk familjebok (Nordic Familybook) and science writer Willy Ley the animal may have survived long enough to be remembered in the legends of the Evenk people of Russia as a huge black bull with a single horn in the forehead. In support of this claim, it has been noted that the 13th century traveller Marco Polo claimed to have seen a unicorn in Java, but his description makes it clear to the modern reader that he actually saw a Javan Rhinoceros. Perhaps additional supporting evidence can be found in the fact that a rhinoceros' horn reacts with alkaloids by turning a different color. A majority of the medieval poisons were made from alkaloids, which coincides with the myth that unicorn horns change color when a poison is placed within them.
Genetic disorders of horned animals seem to be a newly discovered possibility for the inspiration of the unicorn; the idea came in 2008 with the discovery of a roe deer in Italy with a single horn. Single-horned deer aren't unheard of; however, the placement of this horn, in the center of the head, is quite unusual. Fulvio Fraticelli, scientific director of Rome's zoo, has said "Generally, the horn is on one side (of the head) rather than being at the center. This looks like a complex case." Fraticelli also acknowledges that the placement of the horn could have been the result of some type of trauma in the life of the deer.