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Villagers construct a new bridge over the Apurimac River, in Huinchiri, Peru, in 2012. (Federico Tovoli)

The Earliest and Greatest Engineers Were the Incas

Smithsonian Secretary G. Wayne Clough treks to Peru to see how Machu Picchu was built

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In American universities, engineering students typically learn that military and civil engineering originated in Europe, and they study the European tradition almost exclusively—with maybe a glance back at Egypt or China. But the Inca, whose great era of imperial expansion ran roughly from 1438 to 1533, were also master builders, and Smithsonian-affiliated researchers are now bringing their accomplishments to light.

I saw examples of Incan engineering prowess firsthand when I visited Peru in 2011. I walked segments of what was once a 24,000-mile network of roads and gazed in amazement at civil and religious works perched atop, or on the sides of, steep mountains near Cuzco, the Incan capital. The structures at Machu Picchu are the best-known of the Incan triumphs, but there is so much more.

In November, the American Indian Museum hosted a public symposium on Incan engineering accomplishments and the lessons they hold for builders today, particularly in the area of sustainability.

MIT professor John Ochsendorf, one participant, has become an authority on the rope bridges built to traverse the gorges in the Andes—bridges so awe-inspiring that upon seeing them, neighboring peoples would sometimes submit to the Inca without a fight. Later, conquistadors would be reduced to crawling, petrified, across the swaying rope contraptions, although they could bear the weight of columns of soldiers.

Ochsendorf has studied historical records, built a replica bridge and visited the last remaining Incan bridge, in remote Huinchiri, Peru. It is fashioned from native grasses woven into threads, in turn braided into ever-bigger ropes. Each year nearby villagers ceremoniously cut down the existing bridge, let it float away—it’s 100 percent biodegradable—and replace it.

Ochsendorf’s tests suggest that the bridge’s main cables can support 16,000 pounds, and he believes the cables of the sturdiest Incan bridges, incorporating leather, vines and branches, could have supported 200,000 pounds.

Christine M. Fiori, associate director of the Myers-Lawson School of Construction at Virginia Tech, began studying Incan roads five years ago, using tools like ground-penetrating radar. She expected to find deep foundations but didn’t. How could they have survived? “Primarily because the Inca controlled water,” Fiori says: They observed its natural course and directed it, preventing erosion.

As someone who spent 35 years teaching engineering, I know we can learn much from the Inca, who intuitively grasped how to build structures that harmonized with nature. The engineering symposium is part of a broad effort at the American Indian Museum to explore the complex relationship between Incan technology and culture that will culminate in a grand exhibition, in 2015, devoted to the Incan Road.

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