Animals had been written about for centuries before the Christian era, but it was Christianity that took the stories and made them into religious allegories. The first known text to do this was the Physiologus, written in Greek in Alexandria in the second or third century CE. This collection of animal lore is explicitly Christian; it briefly describes an animal, and continues with an Christian allegorical interpretation. The Physiologus was a “bestseller” that was translated into most of the major languages of Europe and western Asia; it is said that it was the most widely-distributed book in Europe after the Bible. Many variations on the text appeared over the centuries. The original Physiologus text, describing less than 50 animals, continued to evolve, accumulating more beasts and additional moral interpretations. Around the seventh century, Isidore of Seville wrote his Etymologiae, an encyclopedia of which part was about animals, derived from the books of Classical authors such as Pliny the Elder. When thePhysiologus combined with the Etymologiae and other texts, the book known as the bestiary was born.
The bestiary, or “book of beasts”, is more than just an expansion of the Physiologus, though the two have much in common. The bestiary also describes a beast and uses that description as a basis for an allegorical teaching, but by including text from other sources it goes further; and while still not a “zoology textbook”, it is not only a religious text, but also a description of the world as it was known.
The bestiary manuscripts were usually illustrated, sometimes lavishly, as for example in the Harley Bestiary and the Aberdeen Bestiary; the pictures served as a “visual language” for the illiterate public, who knew the stories – preachers used them in sermons – and would remember the moral teaching when they saw the beast depicted. Bestiary images could be found everywhere. They appeared not only in bestiaries but in manuscripts of all kinds; in churches and monasteries, carved in stone both inside and out, and in wood on misericords and on other decorated furniture; painted on walls and worked into mosaics; and woven into tapestries. – David Badke, editor, The Medieval Bestiary Index