Bestiary, type of book, popular in the Middle Ages, that purported to describe all the animals in creation, real or imaginary, and the human traits they exemplify. Bestiaries were the source of stories about the unicorn and the Phoenix; such tales were used as Christian allegories for moral and religious instruction. Often illustrated, bestiary tales inspired the animal symbolism used by medieval architects, painters, and sculptors. The prime source of the bestiary was an anonymous mid-2nd-century Greek work, Physiologus (The Naturalist), which was translated into many European languages. Modern variants have been written by such authors as Lewis Carroll, James Thurber, and Jorge Luis Borges.