| (From Latin bestia, beast; cf. bestiarius, a gladiator who fought with animals)
A compilation of tales and anecdotes about animals, quite popular in the Middle Ages. It might be best to think about them as primitive zoological textbooks with heavy mythological leanings.
Included were a mixture of fantastic and real animals, from the common beaver to the great oriental phoenix. There were many versions available, but most tended to agree on basic descriptive tenets.
A sample entry might run as follows (the text is my translation from the Latin text given at the Aberdeen Bestiary project online):
The Phoenix
The Phoenix is a bird from Arabia, called such either because it has the 'Phoenician' (purple) color, or because in the whole world it is unique. This bird lives more than 500 years, and when it feels itself growing old, it collects stacks of branches of a fragrant wood and builds for itself a pyre; turning its wings in the direction of the sun, it feeds the flames by flapping, and burns itself.
But lo, after nine days it rises again from the ashes. The nature of this bird is born by our Lord Jesus Christ, who said 'I have the power of laying down my life, and taking it up again'. If therefore the Phoenix has the power over life and death, why are men so foolish as to mistrust the word of God, who is the true Son of God and said 'I have the power of laying down my life, and taking it up again'. For as our saviour he descended from heaven and replenished the sweet frangrance of the new and old testament. And in the name is God the Father offered himself to us, and on the third day rose again.
The Phoenix thus symbolises the resurrection of the righteous, who, having collected the sweet scent of virtue, prepare for their resurrection after death.
As you can tell, the stories are highly developed in a Christian context, and are meant to highlight basic tenets of the faith. | 
