(also Bestiary), an ancient collection of stories about nature. Based on works from classical Greece and Rome and from the East, the Physiologus first appeared in the second or third century A.D., probably in Alexandria.

The Old Russian Physiologus, which exists in 15th-century copies, derives from a Bulgarian translation from the Greek made in the 11th or 12th century. The work contains information on beasts and birds, such as the lion and eagle; on mythical beings, such as the phoenix, centaur, and siren; and on rocks and trees. The stories are accompanied by commentary in the spirit of medieval Christian symbolism. Many of the stories were made use of in Old Russian literature, icon painting, and manuscript illumination.