The Bestiarius, De Bestiis, or Book of Beasts consists of descriptions and tales of animals, birds, fantastic creatures, and stones, real and imaginary, which are imbued with Christian symbolism or moral lessons. The rising of the phoenix from the pyre, for example, is related to Christ's Resurrection. The bestiary, in all its varied manifestations, enjoyed great popularity during the twelfth and thirteenth centuries, especially in England. Among the most beloved of picture books, a favourite of the literate laity, it functioned as a library and school book and as homiletic source material. The text was frequently illustrated, in styles catering to a variety of purses, and motifs drawn from it are widely encountered in other decorative contexts, including bas-de-page scenes, heraldry, and encyclopaedic world maps (see mappa mundi ). The core of the text originated in the writings of authors such as Herodotus, Aristotle, and Pliny the Elder, and in a Greek text known as the Physiologus (The Natural Philosopher), which is thought to have been compiled in Alexandria around the second century by a Christian ascetic. In the Physiologus, discussions of the characteristics of almost fifty creatures, plants, and stones, along with the etymologies of their names, were distilled from classical mythology and the Christian tradition. The Physiologus was influential for a thousand years, being translated into Arabic, Armenian, Ethiopic, Syriac, and other vernacular languages; the later medieval bestiaries descended primarily from a variable Latin translation that was available from at least the fifth century. Several more beasts and additional material were conflated with the Latin Physiologus from the Etymologies of the seventh-century Spanish bishop Isidore of Seville and other selected sources. From this expanded text, Philippe de Thaon produced a rhyming version in Anglo-Norman (c. 1125), dedicated to Aelis (or Adela) de Louvain, second wife of Henry I of England; this version gave rise to the popular medieval Bestiaire. Other medieval versions include that of Gervaise, written in French (perhaps in Normandy) in the thirteenth century; that of Guillaume le Clerc (the most popular version), written in the early thirteenth century in French by a Norman priest working in England; and two versions ascribed to Pierre de Beauvais, 'le Picard', composed in the dialect of Picardy, also in the early thirteenth century. The Latin bestiary still flourished alongside its French counterparts and was often produced in luxurious illustrated copies in England during the twelfth and thirteenth centuries. These are grouped into two important families on the basis of variations in their texts and programs of illumination.