The Franciscan order, founded by St Francis, was a 'mendicant order' or order of preaching friars who devoted themselves to an active life preaching to the laity. They, along with the Dominicans, were part of a new movement of preaching in the 13th century which represented a response to the growing importance of towns and cities and the social changes that went along with them. The friars developed techniques for preaching that would be helpful in communicating theology and the proper practice of spiritual devotion to their audiences. Bonaventura (1221-1274), an early follower of St Francis, wrote the 'Tree of Life' ('Lignum Vitae') as an aid for presenting meditation upon the sufferings of Christ as an essential spiritual exercise for laity. Diagrams like this one helped the preaching friar organise his thoughts and communicate them more effectively. These pictures rapidly became widespread and popular all over western Europe. By the 14th century, they were being used in England, as in this example in a manuscript from Durham. The tree holds the crucified Christ, his wounds bleeding, and sprouts twelve branches. Each branch is labelled with stages of the Passion or suffering of Jesus when he died. At their ends, the branches grow leaves which represent the 'fruit' of the tree in the form of virtues such as patience for the Christian who contemplates each stage. Figures of prophets and apostles surround the tree, connecting it with words of the Bible. At its top, a pelican wounds its own breast so that its young, shown around it, may feed on its blood. The bleeding pelican was a symbol of the suffering Christ, underscoring the idea of his death for the salvation of his spiritual 'offspring', Christian believers.