The idea of an animal with a single horn projecting from the centre of its forehead, which is the universally accepted definition of a unicorn, is firmly grounded in prehistoric reality. The giant mammal Elasmotherium flourished on the Eurasian continent particularly the steppes and forests of southeastern Russia, Mongolia and northern China. It was even larger than a modern day elephant and had a single horn which grew from the centre of its forehead and measured up to two metres in length.
This real unicorn, whose full scientific designation in Latin is Elasmotherium sibiricum Fischer 25, was a species of rhinoceros. Bjorn Kurtén described the Elasmotherium as "a truly gigantic animal, far larger than any living rhinoceros. It had no nose horn, but instead an immense horn on the forehead: it grew to a length of two metres. This animal was thus a veritable unicorn." (Kurtén, 1968, p. 145).
During the late Pleistocene era the existance of the Elasmotherium and Homo Sapiens overlapped for centuries. It is believed that early encounters with this amazing creature were the basis of stories about the great unicorn. Over time these memories became legends which faded into myth. It is believed that Mediaeval European ideas about the unicorn were ultimately inspired by the mythic Chinese unicorn zhi.
There can be no doubt that during the Medieval era the unicorn was believed to be a real animal. As scientific thought overtook beliefs during the Renaissance sightings of unicorns were attributed to more mundane animal such as rhinos, goats, and horses. Until at last the unicorn was added to the list of animals to be found only in stories and fables.