Dante’s great poem The Divine Comedy embodies a vision of the cosmos consistent with the science of Aristotle and Ptolemy. This is especially evident in the poem’s final part 'Paradiso', in which Dante leaves the earth and visits each celestial sphere in turn, finally reaching the presence of God. On their journey his guide, Beatrice, explains many problems of physical astronomy to the poet. In this picture by Giovanni di Paolo the pair have just left the earth, and Beatrice explains that the universe is a hierarchy of being, all creatures devoid of reason, but above them waits heaven, symbolised by the nine spheres which are ruled by the figure of love. This portrayal of the physical structure of the universe demonstrates the harmony of science and theology in the Middle Ages.