Vitruvius’ De architectura (c. 35–23 BCE) offers an ideal lens through which to view the emergence of the Imperial artes. In the introduction to his work, Vitruvius develops an elaborate theory of architectural knowledge that connects the discipline with other branches of specialized knowledge and gives pride of place to causal explanations of architectural method via natural first principles. Vitruvius’ theory is tailored to architecture but is of wider importance in that it establishes a general notion of ars predicated on the scientific premises sketched in Chapter 2. True to his expansive conception of the discipline, throughout his treatise Vitruvius carefully explains his methods in terms of natural first principles, demonstrating their fundamental soundness. His advice for orienting city streets and walls (Book I) and for choosing building materials (Book II) exemplifies his characteristic interest in connecting architecture with a broader understanding of nature.