The works of Louis I. Kahn were among the greatest influences on world architecture during the second half of the 20th century. Trained in the classical tradition of the Beaux-Arts by Paul Philippe Cret at the University of Pennsylvania, Kahn nevertheless embraced the Modern movement in his early practical experience with various housing authorities and in partnership with Oscar Stonorov and George Howe. Kahn was slow in developing as an architect, and the works of the first 50 years of his life, mostly derived from International Style precedents, did not receive significant notice.

Yet by World War II, Kahn had begun to question the capacity of the International Style to embody contemporary cultural meanings and social institutions. In 1944, Kahn published an essay wherein he defined monumentality in architecture as a spiritual quality conveying a sense of eternity, timelessness, and unchanging perfection. He felt that modern society had failed to give full architectural expression to the institutions of human community, and he pointed to the great monuments of the past, which, although not possible to literally duplicate, embodied the qualities by which all new buildings should be measured. Finally, he indicated the critically important part played by structural perfection and material character in the creation of historical monumental form, calling for a reexamination of contemporary norms of construction. Although he had yet to find their appropriate expression in his architectural designs, Kahn had established what would be the key themes of his career.

Kahn first gained notice not as an architect but as a professor of design at Yale University, starting in 1947. His inspired teaching led to his appointment in 1950 as the architect-in-residence at the American Academy in Rome. Kahn spent much of this time traveling in Italy, Greece, and Egypt, and this period of historical rediscovery would prove to be pivotal in his development as the most important modern architect of his time. The eternal quality of heavy construction and the spaces shaped by massive masonry made a lasting impression on Kahn. Although the building he had completed just prior to leaving for Rome was of steel construction, after this year abroad Kahn never again made use of lightweight steel structures, building only with reinforced concrete and masonry. On his return from Rome, Kahn was commissioned to design the Yale University Art Gallery (1951-53) in New Haven, Connecticut. The first modern building on the Yale campus, its primary street facade was a massive brick wall marked only by concrete string courses at the floor lines. The plan was divided into three primary spaces: two column-free galleries flanking a central service zone where the main stairs, triangular in plan, were housed in a reinforced-concrete cylinder that rose through the four floors to a clerestory light at its top. Kahn's floor structure was likely inspired by the geodesic domes of Buckminster Fuller, yet the triangular grid of poured-in-place concrete, exposed in the ceilings below, was a powerful and heavy presence quite unlike the lightness idealized by Fuller. Incorporating the mechanical and lighting services within their dark pyramidal depths, Kahn's floor structure was also the exact opposite of the structurally and spatially neutral slab heretofore typical of International Style buildings.

The Bath House for the Trenton Jewish Community Center (1954-58) was the project where, as he said, Kahn found himself as an architect. Four pavilions formed a cruciform plan with a court in the center, open to the sky, each pavilion composed of four concrete-block U-shaped hollow piers at the corners, on which sat a pyramidal roof of wood that floated above the heavy earthbound masonry walls enclosing the open-air spaces. For contemporary architects, the Bath House was a revelation—at once modern, built of the most typical of materials, and ancient, a place where earth and sky meet, signified by the unfinished stone circle in its central court.

Although the larger Community Center was never built, the grid of individually roofed volumes was the first design in which Kahn made each space within the complex program into a separate building with its own structure and light. In direct opposition to the undifferentiated free-plan space-in-extension typical of International Style modernism, Kahn now conceived of each function as requiring its own room-as-place, and the plan was now to be understood as "a society of rooms," their spatial relationship articulating their collective purpose.

In 1957, Kahn was appointed to teach at the University of Pennsylvania in Philadelphia, and he began a long and productive association with two remarkable engineers at the university, Robert Le Ricolais, a visionary poet of structure, and at the office, August Komendant, an expert on concrete construction. At this time, he also received the commission for the A. N. Richards Medical Research Building (1955-64) at the University of Pennsylvania and was able to fully develop his concepts of expressive construction and articulate function. Each of the five laboratory towers, a square in plan, was constructed with an elegant precast-concrete cantilevered structure, the columns placed at third points and the structurally independent, load-bearing masonry service shafts located at the midpoints of each side. Exemplifying Kahn's distinction between the "served spaces" (primary function) and the "servant spaces" (services), the floors of each tower were entirely free of structure or services. In what Kahn held to be an ethical imperative, the materials of construction were left exposed, showing how the building was made and becoming the only ornament appropriate to modern building.

The Tribune Review Publishing Company Building (1955—61) in Greensburg, Pennsylvania, was Kahn's first design to demonstrate his emerging understanding of the relationship between structure and light. The main space was spanned by precast-concrete beams, bearing on brick piers, and on the east and west elevations, Kahn revealed the concrete-block walls between these piers to be non-load-bearing by placing glazing between the tops of the walls and the roof structure above, within the depth of the beams. Under these horizontal windows, the in-fill walls were split at their centers by tall, narrow windows, and together these windows produced a T-shaped opening, large at the top to bring in maximum light and narrow at eye level to allow views but to minimize glare.

The First Unitarian Church (1959-69) in Rochester, New York, is directly related to Frank Lloyd Wright's Unity Temple of 1905, indicative of the important influence of Wright's early work on Kahn. Like Wright's design, Kahn's sanctuary is a central, top-lit space enclosed by solid walls, offering no eye-level views out and accessed by a surrounding ambulatory. Yet in the relation of the school to the sanctuary, Kahn took a different approach, ringing the sanctuary with the classrooms. The walls of the sanctuary are made of nonbearing concrete block, the hollow spaces within allowing the return of ventilation air. The roof of the sanctuary is a gently folded plane of cast concrete, lifting to clerestory lights at the corners to form a huge cross shape overhead, and is supported at its center points by columns that stand in each of four doorways from the surrounding ambulatory. The classrooms, also entered from the ambulatory, form a thick protective layer around the sanctuary, their brick exterior walls folded to produce a deeply shadowed edge into which large windows are recessed and small window seats projected.

This concept of surrounding primary spaces with shadow-giving walls, which Kahn described as "wrapping ruins around buildings," emerged fully developed in his design for the Salk Institute (1959-65) in La Jolla, California. This is unquestionably Kahn's greatest design, yet its most important component, the Meeting House, remained unbuilt. The Meeting House plan was also Kahn's first fully developed "society of spaces" plan, a series of independent-room buildings, each with its own geometry and structure, surrounding a central cubic hall. The outer range of rooms facing the ocean assumed the form of hollow cylindrical concrete shells wrapped around and shading cubic glazed rooms within (and vice versa), giving the whole an unparalleled monumentality.

The Salk Institute Laboratories, which were realized, consist of column-free laboratory floors alternating with service floors containing the reinforced-concrete truss structure, the whole constructed of meticulously detailed cast-in-place concrete. Between the two laboratory buildings, where the scientists' wood-clad studies were placed in towers, Kahn envisioned a garden but was convinced by Luis Barragán to make instead a paved plaza, open to the sky and the ocean. Today this plaza, without any formal program of use, remains one of the most powerful and deeply moving spaces ever built.

The Indian Institute of Management (1962-74) in Ahmedabad, India, and the capital of Bangladesh (1962-74) in Dhaka were Kahn's greatest built examples of his "plan as a society of rooms" concept. In both buildings, the secondary spaces, such as corridors, arcades, stair landings, and vestibules, became as important to the overall experience of the building as the primary spaces of program. Kahn understood that learning and decision-making happen not only in the classroom and assembly hall but in the passageways, cafes, and courtyards as well. As Kahn said, he acted as the philosopher for his clients, interpreting their program of uses in ways both culturally resonant and socially suggestive.

The Exeter Academy Library (1965-72) in Exeter, New Hampshire, was Kahn's most subtle and yet revolutionary work in that he turned the traditional program of the library (central reading room surrounded by book stacks) inside out. The design again involved a building-within-a-building, this time a brick load-bearing outer shell, containing the reading spaces, surrounding the inner reinforced-concrete book stacks. In this way, as Kahn said, one could take the book from the protective darkness of the inner stacks to the natural light of the outer reading rooms. At the center of the building, Kahn placed the entry hall, a space that went from ground to sky, with giant circular concrete openings revealing the books, celebrating the purpose of the building.

The Kimbell Art Museum (1966-72) in Fort Worth, Texas, is rightly considered Kahn's greatest built work. The space was composed of a series of concrete vaulted roof forms, each spanning 100 feet, split at their center to allow light to flow in, bouncing off aluminum deflectors to spray the underside of the vaults with an ethereal silver light. Without question, Kahn's most beautiful space, the Kimbell was also the most rigorously resolved example of Kahn's concept of the relation between light and structure, the interior spaces receiving natural light in ways that precisely articulated the structural elements. Finally, the Kimbell was Kahn's most elegant built example of landscape planning, its entry sequence taking us past sunken sculpture gardens, under a vaulted loggia, past sheets of cascading water, through a gravel-floored courtyard filled with a grid of trees, and then quietly into the very heart of the gallery itself.

Many of Kahn's greatest designs were never built, including the Salk Institute Meeting House (1959), the U.S. Angolan Embassy (1959), the Mikveh Israel Synagogue (1961), the Dominican Motherhouse (1965), the Memorial to the Six Million Jewish Martyrs (1966), the Palazzo dei Congressi (1968), and the sublime Hurva Synagogue (1967) in Jerusalem—a group of works that, considered alone, would constitute one of the most significant contributions to 20th-century architecture. Yet even without realizing these astonishing designs, Kahn's importance to the development of modern architecture in the second half of the 20th century cannot be overestimated.

Kahn's work redefined modern architecture in two primary ways. First, by reestablishing the relevance of historical architecture for the design of contemporary buildings, Kahn's work was crucial to the emergence of both the American Postmodern and the European neorational critiques of International Style modernism. Second, by reestablishing the primacy of the art of construction in the design of contemporary buildings, Kahn was critical to the emergence of a "tectonic" interpretation of architectural history and practice. By midcentury, Kahn was one of many who felt that modern architecture had lost its direction and sense of purpose. Yet Kahn stands virtually alone in having opened a way out of this impasse, a way he achieved by reconnecting construction to its ethical imperatives and space making to its ancient origins.

Roserr McCarter

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