There is no more perfect place for a conference on Roman architecture than the majestic Villa Aurelia on the Janiculum Hill in Rome. From the lofty perch of the 17th-century palace’s terrazzo, the Eternal City presents its familiar panoramic splendor. The distinctive silhouette of the Pantheon dome—wide, flat, and ridged—distinguishes itself from the steeper profiles of its neighbors, serving as the archetype of Roman concrete construction at its most transcendent.

Not surprisingly, the Pantheon served as a leitmotif for a gathering to honor William L. MacDonald, who passed away in March 2010 and left an enduring heritage as an inspiring teacher, influential scholar, and unforgettable friend. The Pantheon was MacDonald’s Holy Grail. And “Paradigm and Progeny: Roman Imperial Architecture and its Legacy,” a conference hosted at the villa by the American Academy in Rome in December, further revealed that MacDonald’s quest to understand the Pantheon uncovered architectural design ideas very much in practice today.

MacDonald fathomed as did few others the essence of Roman architecture and shared his knowledge with warmth and generosity. In his writings and in his virtuoso lectures at Yale University in Connecticut and Smith College in Massachusetts, MacDonald defined Roman architecture in a singular language that he created for that purpose. His evocative prose is well demonstrated in, as one conference participant put it, “the most influential book on Roman architecture of the second half of the 20th century”: The Architecture of the Roman Empire I: An Introductory Study (1965).

So critical is MacDonald’s language to his legacy that the symposium’s sessions were organized to track his major works. A session titled “Urban Armature: The City Shaped” neatly fit MacDonald’s 1986 The Architecture of the Roman Empire II: An Urban Appraisal, in which he developed the concept of armature to explain urban design in ancient Rome. A session called “Hadrian and the Empire” expanded the ideas that surfaced in 1995’s Hadrian’s Villa and its Legacy, which MacDonald wrote with John Pinto, who, along with Diane Favro and Fikret Yegül, organized the conference. The sessions were supplemented by a forum moderated by Pinto and Academy director Christopher Celenza, who together engaged three noted architects—Frederick Fisher; Stephen Kieran, FAIA; and Laurie Olin, Hon. AIA—on the relevance of ancient Roman architecture to contemporary design.

Those architects reached consensus on at least one thing: Bill MacDonald mattered because he was an architect’s architectural historian. He was driven by the qualities that absorb architects, including space, volume, light, materials, and technical innovation. “Bill wrote about Roman architecture in a way modern designers could understand,” Olin said. MacDonald himself affirmed in The Architecture of the Roman Empire that “in the study of architecture there can be no substitute for leaning against one’s buildings.” Especially memorable for a discussion within the architecture field—one that is rapidly transitioning to digital modeling—was the architects’ exhortation to draw. “One can’t think as an architect without drawing,” Kieran said. Fisher added, “I always see something better when I draw it.”

MacDonald also looked and saw. He carried scaled drawings of major buildings such as the Pantheon in his pocket and fixed the structures he saw in his mind’s eye by photographing them. (Three thousand images from his well-known collection are now housed at Princeton University.) So thoroughly had the historian embraced the architect’s thinking and vision that MacDonald planned to write (but did not complete) an 11th book to Vitruvius’s 10-volume treatise on architecture.

One objective of the symposium was to assess new directions in Roman architectural studies; a perpendicular concern was the impact of ancient Roman buildings on later architecture. MacDonald worked at the intersection of those interests. The conference scholars steered subjects long associated with MacDonald toward contemporary issues, demonstrating the innovative tools employed for research today. In one paper delivered for the session called “Rome Builds,” inspired by MacDonald’s The Pantheon, Design, Meaning, and Progeny (1976), University of Pennsylvania professor Lothar Haselberger disregarded the interior of the Pantheon’s celebrated dome in favor of the columns on the temple’s façade. Using those columns to underscore the wisdom of MacDonald’s commitment to close visual analysis, Haselberger showed that the original granite column shafts vary in diameter, while the Corinthian capitals vary in height. Haselberger explained these disparities—documented through laser scanning by the Bern Digital Pantheon Project—as the result of the complexity of the building program, scale of the temple, reliance on outsourcing, carving of the columns by hand, and quest for dramatic visual effect.

Northwestern University professor emeritus James Packer—who, in 2010, launched a digital recreation of the Roman Forum—applied the urban armature concept that MacDonald developed in 1986 to the evolution of the Forum. According to MacDonald, the streets, plazas, and key public buildings of Roman metropolitan centers formed urban armatures, whose components accumulated over time in response to what he characterized as “the universal urban need for an architecture of connection and passage.” MacDonald differentiated urban armatures from city plans, which had a theoretical basis and were laid out all at once. Packer’s treatment of the Forum’s architectural development, the most comprehensive to date, associates the Forum with armatures deployed in such frontier municipalities as Palmyra (Syria).

The opus reticulatum at Hadrian’s Villa at Tivoli, Italy, admired by today’s designers for its netlike pattern, was waning as a concrete facing by 120 C.E., according to York University professor emeritus Guy Métraux; it may have exemplified a nostalgia sometimes present in private villa architecture. Elizabeth Fentress, president of the International Association for Classical Archaeology in Rome, revealed interesting details about “other villas” belonging to Hadrian at Anagni and Praeneste that further expand MacDonald’s work at Tivoli, but also make apparent that Hadrian’s Villa remains unique.

The formal program concluded with a presentation by University of California at Santa Barbara professor Fikret Yegül, which stood out as the most MacDonald-like of the conference’s many papers. Yegül pronounced the column to be the principal gene of Classical architecture. Elegantly simple, with base, shaft, and capital, the column was used for structural, aesthetic, and symbolic purposes—alternatingly and even simultaneously. Ubiquitous in the ancient world, the column could be endlessly duplicated, as the preserved streets of Roman Palmyra attest. The Romans were skilled at using this fundamental module of Classical architecture in traditional ways (to hold up an architrave, for example) but also deployed the column in innovative configurations. Experiments in Rome began with the projecting columnar bays of the Forum Transitorium and the pilasters supporting broken triangular pediments in the hemicycle of the Markets of Trajan—culminating in such pulsating “baroque” façades as that of the Theater at Sabratha (Libya).

By focusing through his writings on the Pantheon, Hadrian’s Villa, and the Roman provinces under Trajan and Hadrian, MacDonald illuminated Hadrian as both a patron of architecture and an amateur architectural practitioner known for sketching vaults in the form of gourds. The Roman architect Rabirius may have inspired Hadrian’s famous “pumpkin” domes; Rabirius certainly inspired MacDonald, who playfully signed his name, along with those of other Classical architects, to postcards that he sent to colleagues and friends. While MacDonald’s work on the Pantheon and other major Roman buildings defined his legacy as an architectural historian, it was MacDonald’s close and personal association with his subject—with architecture, and with architects—that cemented his reputation among designers working nearly two millennia later.