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Amazon: Archaeological wonder or alien crop circles?

New discoveries suggest the Amazon was home to civilizations that rivaled classical Greece.

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RIO BRANCO, Brazil — It’s not every day a traveler casually looks out an airplane window and discovers the ruins of an unknown ancient civilization.

“I said, ‘Wow, what am I seeing?’” said Alceu Ranzi, a geographer and paleontologist with the Federal University in the Brazilian state of Acre. “This is not natural.”

What he saw that afternoon in 1999 was a giant, geometrically precise circle carved in the earth. Nearly invisible from the ground, the earthwork had only recently emerged when farmers cleared a tract of forest. The huge structures suggested the area may have been home to many more people than anyone previously believed.

“It’s something new that no one expected,” Ranzi said. “No one expected that a discovery of this level still could have happened in that region.”

Ranzi recruited a team of archaeologists from Brazil and Finland and began searching for more of these earthworks, which he calls geoglyphs.

Their work on the ground in this Brazilian border state has recently received an unlikely boost from space. New Google Earth images this year revealed even more of the formations. The scientists now say they’ve tallied 300 massive shapes — circles, squares, rectangles — scattered across 3,900 square miles.

Ranzi said the size and breadth of the discovery reveals that, some 1,000 years ago, the region was home to a large, complex society. The find has expanded a rapidly growing body of archaeological evidence suggesting that the Amazon — once thought to be largely wild in antiquity — was home to civilizations that may have rivaled those of the ancient West.

“It could be something as important as an unknown Roman empire, or a Mesopotamia,” Ranzi said. “It was completely covered by the forest for six or 10 centuries and now is reappearing.”

Proving this will take decades more work, he said. Scientists are only just beginning to document the size and scope of ancient societies in Amazonia, a region roughly the size of the continental United States. Years after seeing his first geoglyph, Ranzi said he’s only beginning to understand its purpose.

The glyphs are geometrically perfect shapes, usually two to three football fields wide and sketched on earth with giant ditches that average 35 feet across and 3 to 10 feet deep. Soil piled alongside created banks 1.5 to 3 feet high.

They date to between 850 and 1,000 years ago, Ranzi said. So far scientists have found little evidence of human habitation inside the shapes, leading researchers to suspect they were used for ceremonies and kept clean.

And, based partly on the tremendous amount of manpower it would have taken to dig the ditches, researchers estimate that at least 90,000 people might have lived among the 300 glyphs so far identified. Up to this point, scientists have only been able to explore deforested land, so they suspect they’ve documented barely more than a tenth of existing geoglyphs.

The importance of these shapes goes beyond what they reveal about a civilization inhabiting this particular corner of the jungle. They’re part of a rising tide of evidence that’s overturning long-held assumptions about the history of the entire Amazon basin.