The diverse collection of essays presented in this volume grew out of the international conference “Proportional Systems in the History of Architecture,” held in Leiden in March 2011 (Fig. 1). The conference was scheduled to commemorate the sixtieth anniversary of the last international conference on proportional systems in the arts, held in Milan in 1951 and titled “De divina proportione,” which similarly gathered leading thinkers of its day (Fig. 2). This anniversary thus offers a valuable opportunity to reflect on where the study of proportional systems has gone over the past sixty years, and where it might most productively go from here. Although the premises of the two conferences were fundamentally different from one another—the Milan conference promoted the contemporary use of proportional systems in the arts for the aesthetic and spiritual betterment of society, while the Leiden conference promoted the historical study of specifically architectural proportional systems for the advancement of scholarly knowledge—certain noteworthy attitudes toward the subject of proportional systems manifested in the Milan conference are still prominent today. Both conferences together demonstrate a sustained recognition of the importance of the multidisciplinary study of proportional systems as integral parts of human culture across time and geography. Less productively, while sympathy with the overtly mystical beliefs that drove the Milan conference is substantially more subdued in the scholarly community today, a fundamental ambiguity inherent in the concept of proportion that enabled those beliefs to flourish in 1951 continues to characterize much scholarly thinking about this subject today: when architectural historians use the word “proportion,” whether they intend it to signify a ratio, architectural beauty, or both simultaneously, is often unclear to author and reader alike.

This introduction will explore this ambiguity, and propose a clarification of it to serve as a common thread tying together the two editorial premises of this volume: first, that there is no causal relationship between proportional systems and the aesthetic qualities of architecture; and second, that proportional systems, as non-visual bearers of meaning and objects of belief, contributed to the rhetorical rather than visual structure of architecture prior to the advent of modern structural engineering, which Rowland Mainstone dates to 1742–1743. Proportional systems during this long period may thus be understood as having served no practical purposes, but nevertheless to have played critical roles in distinguishing architecture from mere building.