Mediaeval philosophers also saw allegory in the natural world, interpreting animals, plants, and even non-living things in books called bestiaries as symbols of Biblical figures and morals. For example, one bestiary compares stags with people devoted to the Church, because (according to medieval zoology) they leave their pastures for other (heavenly) pastures, and when they come to broad rivers (sin) they form in line and each rests its head on the haunches of the next (supporting each other by example and good works), speeding across the waters together.