Indeed, the ground seemed to slope downward for a long stretch, then tilt upward again, as if someone had carved out an enormous ditch.

“It’s a moat,” Heckenberger said.

“What do you mean, a moat?”

“A moat. A defensive ditch.” He added, “From nearly nine hundred years ago.”

Pinage and I tried to follow the moat’s contours, which curved in a nearly perfect circle through the woods. Heckenberger said that the moat had originally been between a dozen and sixteen feet deep, and about fifty feet wide. It was nearly a mile in diameter. I thought of “the long, deep ditches” that the spirit Fitsi-fitsi was said to have built around settlements. “The Kuikuros knew they existed, but they didn’t realize that their own ancestors had built them,” Heckenberger said.

Afukaká, who had helped with the excavation, said, “We thought they were made by the spirits.”

Heckenberger walked over to a rectangular hole in the ground, where he had excavated part of the moat. Pinage and I peered over the edge with the chief. The exposed earth, in contrast to other parts of the forest, was dark, almost black. Using radiocarbon dating, Heckenberger had dated the trench to about 1200 A.D. He pointed the tip of his machete to the bottom of the hole, where there seemed to be a ditch within the ditch. “That’s where they put the palisade wall,” he said.

“A wall?” I asked.

Heckenberger smiled and went on, “All around the moat, you can see these funnel shapes, equally spread apart. There are only two explanations. Either they had traps at the bottom or they had something sticking into them, like tree trunks.”

He said that the concept of traps made little sense, since the people the moat was supposed to be protecting would have been in peril themselves. What’s more, he said, when he examined the moats with Afukaká, the chief told him a legend about a Kuikuro who had escaped from another village by leaping over “a great palisade wall and ditch.”

Still, none of it seemed to make sense. Why would anyone build a moat and a stockade wall in the middle of the wilderness? “There’s nothing here,” I said.

Heckenberger didn’t respond; instead, he bent down and rooted through the dirt, picking up a piece of hardened clay with grooves along the edges. He held it up to the light. “Broken pottery,” he said. “It’s everywhere.”

As I looked at other shards on the ground, I thought of how Fawcett had once asserted in a letter that on certain high grounds in the Amazon “very little scratching will produce an abundance” of ancient pottery.

Heckenberger said that we were standing in the middle of a vast ancient settlement.

“Poor Fawcett—he was so close,” Pinage said.

It was understandable why Fawcett wouldn’t have been able to see it, Heckenberger went on. “There isn’t a lot of stone in the jungle, and most of the settlement was built with organic materials—wood and palms and earth mounds—which decompose,” he said. “But once you begin to map out the area and excavate it you are blown away by what you see.”

He began walking once more through the forest, pointing out what was, increasingly clearly, the remains of a massive man-made landscape. There was not just one moat but three, arranged in concentric circles. There was a giant circular plaza where the vegetation had a different character than that of the rest of the forest, because it had once been swept clean. And there had been a sprawling neighborhood of dwellings, as evidenced by even denser black soil, which had been enriched by decomposed garbage and human waste.

As we walked around, I noticed an embankment that extended into the forest in a straight line. Heckenberger said that it was a road curb.

“They had roads, too?” I asked.

“Roads. Causeways. Canals.” Heckenberger said that some roads had been nearly a hundred and fifty feet wide. “We even found a place where the road ends at one side of a river in a kind of ascending ramp and then continues on the other side with a descending ramp. Which can mean only one thing: there had to have been some kind of wooden bridge connecting them, over an area that was a half mile long.”

They were the very same kind of dreamlike causeways and settlements that the Spanish conquistadores had spoken of when they visited the Amazon, in which Fawcett had so fervently believed and which twentieth-century scientists had dismissed as myths. I asked Heckenberger where the roads led, and he said that they extended to other, equally complex sites. “I just took you to the closest one,” he said.

Altogether, he had uncovered twenty pre-Columbian settlements in the Xingu. The settlements were about two to three miles apart and were connected by roads. More astounding, the plazas were laid out along cardinal points, from east to west, and the roads were positioned at the same geometric angles. (Fawcett said that Indians had told him legends that described “many streets set at right angles to one another.”)

Borrowing my notebook, Heckenberger began to sketch a huge circle, then another and another. These were the plazas and the villages, he said. He then drew rings around them, which he said were the moats. Finally, he added several parallel lines that jutted out from each of the settlements in precise angles—the roads, bridges, and causeways. Each form seemed to fit into an elaborate whole, like an abstract painting viewed from a distance. “Once my team and I started to map everything out, we discovered that nothing was done by accident,” Heckenberger said. “All these settlements were laid out with a complicated plan, with a sense of engineering and mathematics that rivalled anything that was happening in much of Europe at the time.”

Heckenberger said that each cluster of settlements contained anywhere from two thousand to five thousand people, which means that the larger community was the size of many medieval European cities. “These people had a cultural aesthetic of monumentality,” he said. “They liked to have beautiful roads and plazas and bridges. Their monuments were not pyramids, which is why they were so hard to find; they were horizontal features. But they’re no less extraordinary.”

Heckenberger’s discoveries have been documented in numerous scholarly journals; in 2003, he published a paper in Science titled “Amazonia 1492: Pristine Forest or Cultural Parkland?” He also recently published a book detailing his discoveries, called “The Ecology of Power.” His work has been hailed as proof that the rain forest once contained civilizations nearly as rich and complex as those of the Inca and the Maya and Europeans. And Heckenberger has helped to upend the view of the Amazon as a counterfeit paradise that could never sustain what Fawcett had envisioned: a prosperous, glorious civilization.

Others have fuelled this revolution in archeology. Anna Roosevelt, a great-granddaughter of Theodore Roosevelt, who is an archeologist at the University of Illinois, has discovered, along the floodplains of the Amazon, buried settlements that may be eleven thousand years old. Scientists have also begun to find enormous man-made earth mounds scattered across the region. Geologists have uncovered so much black earth from ancient settlements that they now believe the Amazon may have sustained millions of people. One prominent scholar, Donald Lathap, even argues that the Amazon may have been the wellspring of high civilization throughout the Americas—that an advanced culture had spread outward, rather than vice versa.