Behind every great architect there is a great engineer. Or more accurately, behind every great modern architect there is a great engineer, for until the twentieth century, the two professions were one. The accomplished—and largely anonymous—medieval master-masons who built the Gothic cathedrals, for example, were responsible equally for ornament and structure, which may be why it is often hard to distinguish between the two. The pointed arch, as the British scholar John Summerson observed years ago, is as much fanciful as functional, and what appear to be structural ribs in the stone ceilings are strictly decorative. On the other hand, window tracery made of lead and iron, while forming a pretty pattern, effectively resists gravity and wind forces; and although the stone piers that line the nave are designed to resemble bundled columns—a visual conceit—their mass is needed to support the great weight of the wall and the stone ceiling above. In a medieval cathedral, architecture and engineering are crucially combined.
The architects of the Renaissance, although sometimes less interested in structural virtuosity, were equally versed in construction. In his famous treatise On the Art of Building in Ten Books, Leon Battista Alberti devoted one entire book to the subject, and another to “Public Works,” that is roads, bridges, underground drains, and fortifications, which were all among the work undertaken by architects. The union of architecture and engineering continued for centuries. Christopher Wren designed and built the ingenious triple dome of St. Paul’s Cathedral in London, and a hundred years later, Thomas Ustick Walter designed the immense dome of the Capitol in Washington, D.C., whose form was modeled on St. Peter’s in Rome although it was built of cast iron.
The material that brought about a major change in the relationship between architecture and engineering was reinforced concrete. Concrete had been known for centuries—the Romans used pozzolana, a natural mixture of volcanic silica, lime, and fired rubble, as cement mortar and concrete. The manufacture of artificial cement (“Portland cement”) was introduced in Britain in the mid-nineteenth century. In the late 1800s three French inventor-builders, Joseph Monier, Edmond Coignet, and François Hennebique, independently discovered that concrete—strong when compressed but weak when stretched or bent—could be reinforced with iron and steel bars. The result, which combined the compressive strength of concrete with the tensile strength of steel, was fireproof, relatively cheap, and could be cast in a variety of shapes.
Both Monier and Hennebique built bridges out of reinforced concrete, but it was Robert Maillart, a Swiss engineer and a student of Hennebique, who was the first master of the new material. He built a series of light, elegant Alpine bridges whose extraordinary beauty is impressive, one hundred years later. Immediately after World War I, the engineer Eugène Freyssinet tested the limits of the new material still further when he designed two airship hangars for Orly Airport whose thin concrete vaults were three hundred feet wide and two hundred feet high—the …