An Inca suspension bridge in 1877 and the George Washington Bridge over the Hudson. Engraving, from “Peru: Incidents of Travel and Exploration in the Land of the Incas” by E. George Squier (Harper and Brothers); Angel Franco/The New York Times
via NYTimes:
How the Inca Leapt Canyons
By JOHN NOBLE WILFORD
Published: May 8, 2007
CAMBRIDGE, Mass. — Conquistadors from Spain came, they saw and they
were astonished. They had never seen anything in Europe like the
bridges of Peru.
Chroniclers wrote that the Spanish soldiers stood in awe and fear
before the spans of braided fiber cables suspended across deep gorges
in the Andes, narrow walkways sagging and swaying and looking so frail.
Yet the suspension bridges were familiar and vital links in the vast
empire of the Inca, as they had been to Andean cultures for hundreds of
years before the arrival of the Spanish in 1532. The people had not
developed the stone arch or wheeled vehicles, but they were
accomplished in the use of natural fibers for textiles, boats, sling
weapons — even keeping inventories by a prewriting system of knots.
So
bridges made of fiber ropes, some as thick as a man’s torso, were the
technological solution to the problem of road building in rugged
terrain. By some estimates, at least 200 such suspension bridges
spanned river gorges in the 16th century. One of the last of these,
over the Apurimac River, inspired Thornton Wilder’s novel “The Bridge
of San Luis Rey.”
Although scholars have studied the Inca road
system’s importance in forging and controlling the pre-Columbian
empire, John A.Ochsendorf of the Massachusetts Institute of Technology here said, “Historians and archaeologists have neglected the role of bridges.”
Dr. Ochsendorf’s research on Inca suspension bridges, begun while he was an undergraduate at Cornell University,
illustrates an engineering university’s approach to archaeology,
combining materials science and experimentation with the traditional
fieldwork of observing and dating artifacts. Other universities conduct
research in archaeological materials, but it has long been a specialty
at M.I.T.
Photos: Carl T. Gossett Jr./The New York Times, left; Adriana von Hagen, center; and Robert Spencer for The New York Times
The first steel section, top, being installed on the Verrazano-Narrows Bridge in 1963. The last remaining Inca bridge in Peru, center, was the model for the M.I.T. bridge project. John A. Ochsendorf of M.I.T., above, showing cable made in Peru.
Students here are introduced to the multidisciplinary
investigation of ancient technologies as applied in transforming
resources into cultural hallmarks from household pottery to grand
pyramids. In a course called “materials in human experience,” students
are making a 60-foot-long fiber bridge in the Peruvian style. On
Saturday, they plan to stretch the bridge across a dry basin between
two campus buildings.
In recent years, M.I.T. archaeologists and
scientists have joined forces in studies of early Peruvian ceramics,
balsa rafts and metal alloys; Egyptian glass and Roman concrete; and
also the casting of bronze bells in Mexico. They discovered that
Ecuadoreans, traveling by sea, introduced metallurgy to western Mexico.
They even found how Mexicans added bits of morning-glory plants, which
contain sulfur, in processing natural rubber into bouncing balls.
“Mexicans
discovered vulcanization 3,500 years before Goodyear,” said Dorothy
Hosler, an M.I.T. professor of archaeology and ancient technology. “The
Spanish had never seen anything that bounced like the rubber balls of
Mexico.”
Heather Lechtman, an archaeologist of ancient technology
who helped develop the M.I.T. program, said that in learning “how
objects were made, what they were made of and how they were used, we
see people making decisions at various stages, and the choices involve
engineering as well as culture.”
From this perspective, she said,
the choices are not always based only on what works well, but also are
guided by ideological and aesthetic criteria. In the casting of early
Mexican bells, attention was given to their ringing tone and their
color; an unusually large amount of arsenic was added to copper to make
the bronze shine like silver.
“If people use materials in
different ways in different societies, that tells you something about
those people,” Professor Lechtman said.
In the case of the
Peruvian bridges, the builders relied on a technology well suited to
the problem and their resources. The Spanish themselves demonstrated
how appropriate the Peruvian technique was.
Dr. Ochsendorf, a
specialist in early architecture and engineering, said the colonial
government tried many times to erect European arch bridges across the
canyons, and each attempt ended in fiasco until iron and steel were
applied to bridge building. The Peruvians, knowing nothing of the arch
or iron metallurgy, instead relied on what they knew best, fibers from
cotton, grasses and saplings, and llama and alpaca wool.
The Inca
suspension bridges achieved clear spans of at least 150 feet, probably
much greater. This was a longer span than any European masonry bridges
at the time. The longest Roman bridge in Spain had a maximum span
between supports of 95 feet. And none of these European bridges had to
stretch across deep canyons. [read on...]
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