On July 24, 1911, Yale University lecturer and amateur archaeologist Hiram Bingham completed a steep climb from Peru's Urubamba River valley through the thin air of the Andes Mountains to one of the most significant and lasting discoveries in archeological history—the Inca ruins of Machu Picchu. Perched about 2,400 meters above sea level and 80 kilometers from the onetime Inca capital of Cusco, the "Lost City of the Incas" remained undiscovered by the Spanish throughout their conquest of Peru in the 1500s. As a result Bingham was able to introduce the world to a relatively pristine sanctuary of a once-mighty pre-Columbian empire that would be carefully studied by archeologists, geologists, anthropologists and engineers for a century to come.

Bingham's expedition had traveled to the Urubamba Valley, near the village of Ollantaytambo (today's best surviving example of an Inca town) in search of Vitcos, the last Inca capital before the arrival of Spanish conquistadors. What Bingham instead found was "a remarkably large and well-preserved abandoned city practically untouched by the hands of the spoiler, and apparently unknown to the Spanish chroniclers," Bingham wrote in the March 26, 1914, issue of Nature. (Scientific American is part of Nature Publishing Group.)

During its rediscovery and in subsequent trips to the site, Bingham and his colleagues excavated the ruins at Machu Picchu. "Many difficulties had to be overcome, but we were eventually successful in locating more than one hundred burial caves," Bingham wrote. "The excavation yielded a considerable amount of anthropological material, including human and animal bones, a large number of potsherds and a few stone, silver, and bronze implements." Bingham also noted that he and his colleagues found no gold, the treasure that fueled much of Spain's seemingly insatiable pillaging of the Inca Empire.

"Machu Picchu is in a remarkably good state of preservation, and its architecture has not become confused by Spanish efforts to build churches and villas," as occurred in Cusco and elsewhere, Bingham wrote. "It is safe to say that Machu Picchu was essentially a city of refuge." Given the Incas had no written language, the true purpose of Machu Picchu remains open to debate, with some calling it a government retreat and others convinced that it was a defensive citadel.

Whereas Bingham's archeological finds were a significant breakthrough in the study of pre-Columbian cultures in South America, his handling of these artifacts launched a custody battle between the Yale Peabody Museum and the Peruvian government that has been festering for many decades. Peru claims to have agreed to an 18-month loan to Yale of the ceramic pieces, silver statues, jewelry and human bones that Bingham and his team excavated. Yale argued that the artifacts belonged in a museum where they could be properly maintained and displayed. The museum relented last year and recently sent 350 artifacts back to their native land.

Machu Picchu has since become a Peruvian Historical Sanctuary, UNESCO World Heritage Site and major tourist destination. In order to preserve the site, a no-fly zone was implemented over the ruins, and tourism has been limited in recent years.

In honor of the centennial of Bingham's initial expedition to Machu Picchu, Scientific American presents a slide show of images from the site of the famous ruins as well as the 88-kilometer Inca Trail that stretches from Cusco to the Sun Gate on Machu Picchu Mountain.