AbstractThis paper explores the convergence of musical and architectural theory in Vitruvius’De Architectura.Section 1 describes Vitruvius’ architectural lexicon, borrowed from Aristoxenus (I.2), and explores his description of the laws of harmony, modeled onElementa Harmonica(V.4). Section 2 explores how Vitruvius proposes using music theory in practical architectural design, including construction of columns using architectural orders analogous to Aristoxeniangenera(I.2.6; IV.1); acoustical designs for theatres (V.5); and the development of machines, including siege engines ‘tuned’ like musical instruments (X.12) and water-organs [hydrauli] constructed to execute all the different varieties of tuning (X.8). Section 3 reflects on Vitruvius’ use of analogies with a musical instrument, thesambuca, to explain his understanding of cosmic harmony and architectural form, and his possible sources (VI.1). Finally, Section 4 discusses Vitruvius’ ideas about the importance of a liberal arts education that includes study of music theory. The best architects, Vitruvius explains, can discover in music the secrets to forms they both encounter in nature and create themselves.