Much more than a book on buildings and machines, the contents of De Architectura reveal the ancients' much wider concept of what exactly is 'architecture' and it describes such topics as science, mathematics, geometry, astronomy, astrology, medicine, meteorology, philosophy, and the importance of the effects of architecture, both aesthetic and practical, on the everyday life of citizens. In short, according to Vitruvius, the successful architect and engineer should have both theoretical and practical knowledge based on a broad and deep understanding of all the sciences, arts, and even nature. Even more importantly, for Vitruvius buildings should always be three things: beautiful, stable, and useful.