<P> Unicorns are not found in Greek mythology , but rather in the accounts of natural history , for Greek writers of natural history were convinced of the reality of unicorns , which they believed lived in India , a distant and fabulous realm for them . The earliest description is from Ctesias , who in his book Indika ( `` On India '' ) described them as wild asses , fleet of foot , having a horn a cubit and a half ( 700 mm , 28 inches ) 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 . 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 ( 900 mm , 35 inches ) in length . '' In On the Nature of Animals ( Περὶ Ζῴων Ἰδιότητος , De natura animalium ) , Aelian , quoting Ctesias , adds that India produces also a one - horned horse ( iii. 41 ; iv. 52 ) , and says ( xvi. 20 ) that the monoceros ( Greek : μονόκερως ) was sometimes called cartazonos ( Greek : καρτάζωνος ) , which may be a form of the Arabic karkadann , meaning `` rhinoceros '' . </P>
where did the idea of a unicorn come from
Greek writers of natural history