For thirty years John Onians has been trying to expand and deepen the discipline of art history. His books, Art and Thought in the Hellenistic Age (1979), Bearers of Meaning. The Classical Orders in Antiquity, the Middle Ages and the Renaissance (1988) and Classical Art and the Cultures of Greece and Rome (1999), sought to extend the understanding of art as an aspect of culture, while his current project, A Natural History of Art, is designed to show...