The upper church was built just after the lower church, between 1230 and 1253, and the change in style and grandiosity is readily apparent. One of the most famous pieces of art in the world is the 28-part fresco circling the walls. The fresco has been attributed to Giotto and his pupils for hundreds of years, but the question of who produced it is now under debate within the art-historian community. The fresco starts just to the right of the altar and continues clockwise around the church. Above each image is a biblical fresco with 28 corresponding images from the Old and New Testaments (possibly painted by Giotto, or Pietro Cavallini, who might or might not have painted the fresco cycle). The frescoes in the basilica literally revolutionised art in the Western world. All the gold leaf and flat iconic images of the Byzantine and Romanesque periods were eschewed for natural backgrounds, people of all classes, and a human, suffering Jesus. This was in keeping with Francis’ idea that the human body was ‘brother’ and the earth around him mother and sister.