unusual nicks in their earlobes, the traits I had noticed on the two men accompanying us.
Even as the epidemics hit, Stearman learned, the group was fighting the white cattle ranchers who were taking over the region. The Bolivian military aided the incursion by hunting down the Sirionó and throwing them into what were, in effect, prison camps. Those released from confinement were forced into servitude on the ranches. The wandering people Holmberg traveled with in the forest had been hiding from their abusers. At some risk to himself, Holmberg tried to help them, but he never fully grasped that the people he saw as remnants from the Paleolithic Age were actually the persecuted survivors of a recently shattered culture. It was as if he had come across refugees from a Nazi concentration camp, and concluded that they belonged to a culture that had always been barefoot and starving.
Far from being leftovers from the Stone Age, in fact, the Sirionó are probably relative newcomers to the Beni. They speak a language in the Tupí-Guaraní group, one of the most important Indian language families in South America but one not common in Bolivia. Linguistic evidence, first weighed by anthropologists in the 1970s, suggests that they arrived from the north as late as the seventeenth century, about the time of the first Spanish settlers and missionaries. Other evidence suggests they may have come a few centuries earlier; Tupí-Guaraní–speaking groups, possibly including the Sirionó, attacked the Inka empire in the early sixteenth century. No one knows why the Sirionó moved in, but one reason may be simply that the Beni then was little populated. Not long before, the previous inhabitants’ society had disintegrated.
To judge by Nomads of the Longbow, Holmberg did not know of this earlier culture—the culture that built the causeways and mounds and fish weirs. He didn’t see that the Sirionó were walking through a landscape that had been shaped by somebody else. A few European observers before Holmberg had remarked upon the earthworks’ existence, though some doubted that the causeways and forest islands were of human origin. But they did not draw systematic scholarly attention until 1961, when William Denevan came to Bolivia. Then a doctoral student, he had learned of the region’s peculiar landscape during an earlier stint as a cub reporter in Peru and thought it might make an interesting topic for his thesis. Upon arrival he discovered that oil-company geologists, the only scientists in the area, believed the Beni was thick with the remains of an unknown civilization.
Convincing a local pilot to push his usual route westward, Denevan examined the Beni from above. He observed exactly what I saw four decades later: isolated hillocks of forest; long raised berms; canals; raised agricultural fields; circular, moat-like ditches; and odd, zigzagging ridges. “I’m looking out of one of these DC-3 windows, and I’m going berserk in this little airplane,” Denevan said to me. “I knew these things were not natural. You just don’t have that kind of straight line in nature.” As Denevan learned more about the landscape, his amazement grew. “It’s a completely humanized landscape,” he said. “To me, it was clearly the most exciting thing going on in the Amazon and adjacent areas. It may be the most important thing in all of South America, I think. Yet it was practically untouched” by scientists. It is still almost untouched—there aren’t even any detailed maps of the earthworks and canals.
Beginning as much as three thousand years ago, this long-ago society—Erickson believes it was probably founded by the ancestors of an Arawak-speaking people now called the Mojo and the Bauré—created one of the largest, strangest, and most ecologically rich artificial environments on the planet. These people built up the mounds for homes and farms, constructed the causeways and canals for transportation and communication,