The legend of the unicorn occurs in all medieval cultures, with fabulous, medicinal, allegorical, programmatic, and decorative meanings. The unicorn (Greek: monokeros; Latin: unicornis or rhinoceros; Arabic: karkaddan; Old French: licorne; Middle High German: einhorn or monizirus) is first mentioned by Ctesias (ca. 400 B.C.), a Greek physician at the Persian court, who told of a savage wild ass with a horse's body, a goat's head, and a single, spiral horn. The legend of the unicorn owes its widespread diffusion not to numerous ancient reports (Aristotle, Aelian, Pliny) but to the Physiologus and to patristic commentary on passages in the Vulgate where monokeros (the Septuagint translation of the Hebrew re'em, wild ox or aurochs) is rendered by either unicornis or rhinoceros, whence the equivalence of these two beasts for Jerome, Tertullian, Gregory, and Bede. Latin patristic writers averred parallels between Christ born of the Virgin Mary and the unicorn, which could be captured only by a virgin.
Earlier Greek patristic commentators, in the wake of the First Council of Nicaea (325), interpreted the unicorn's single horn as a symbol of divine unity. Islamic remarks on the karkaddan appear almost exclusively in travelogues with reference either to medicinal or magical properties of the unicorn's horn, to its fierceness, or to the hunt. Islamic commentators assign no religious significance to the unicorn; their belief that the unicorn's horn could detect poison is mentioned in the writings of Hildegard of Bingen, Albertus Magnus, and Pietro d'Abano. The tradition of assigning medicinal properties to the unicorn's horn, dating back to the Greek Physiologus, gained particular currency in the Latin West after the twelfth century. Medieval German writers speak of a jewel at the base of the horn with healing powers.
At this time in the West both the increasingly important vernacular bestiary tradition and the erotic exploitation of the legend--that the proud lover is tamed by his beloved just as the unicorn is captured by a virgin--somewhat eclipsed earlier patristic exegesis. Examples of the vernacular tradition are Guillaume le Clerc's Bestiaire divin (ca. 1210) and Brunetto Latini's Li livres dou tresor (1262-ca. 1265); erotic versions are found as early as the fifth century in the Syriac translation of the Physiologus and are evidenced in the thirteenth century both in Minnedichtung and in Richard de Fournival's Bestiaire d'amour. The extent of this secularization of the unicorn may be attested also in the presence of the unicorn in certain illustrated Hebrew codices, such as Ashkenazi bestiaries and fifteenth-century manuscripts of Issac ben Sahula's Meshal ha-Kadmoni.
Perhaps as a reaction to this growing secularization, some fifteenth-century interpreters viewed the hunt of the unicorn as an allegory of the Annunciation in the hortus conclusus (enclosed garden). This late tradition underscores the wealth and freedom of medieval interpretations and applications of the unicorn. No iconographical prototype from classical art influenced the depiction of the unicorn: a late-fourth-century Syrian church mosaic is the earliest representation thus far uncovered. In Islamic art the unicorn is primarily decorative. Illustrated Physiologus manuscripts concentrate on the hunt of the unicorn. Late medieval ivory caskets juxtapose programmatically the slaying of the unicorn with the tryst of Tristan and Isolde in the orchard. The fifteenth-century "Hunt of the Unicorn" tapestries at the Cloisters, New York, do not seem as programmatic as the "Dame à la licorne" tapestries at the Musée de Cluny, Paris, which, according to Alain Erlande-Brandenburg, depict a renunciation of the uncontrolled senses.