WASHINGTON — The Amazon River basin was not all a pristine, untouched wilderness before Columbus came to the Americas, as was once believed. Researchers have uncovered clusters of extensive settlements linked by wide roads with other communities and surrounded by agricultural developments.

The researchers, including some descendants of pre-Columbia tribes that lived along the Amazon, have found evidence of densely settled, well-organized communities with roads, moats and bridges in the Upper Xingu part of the vast tropical region.

Michael Heckenberger, first author of the study appearing this week in the journal Science, said the ancestors of the Kuikuro people in the Amazon basin had a "complex and sophisticated" civilization with a population of many thousands during the period before 1492.

"These people were not the small mobile bands or simple dispersed populations" that some earlier studies had suggested, he said.

Instead, the people demonstrated sophisticated levels of engineering, planning, cooperation and architecture in carving out of the tropical rain forest a system of interconnected villages and towns making up a widespread culture based on farming.

Heckenberger said the societies that lived in the Amazon before Columbus were overlooked by experts because they did not build the massive cities and pyramids and other structures common to the Mayans, Aztecs and other pre-Columbian societies in South America.

Instead, they built towns, villages and smaller hamlets all laced together by precisely designed roads, some more than 50 yards across, that went in straight lines from one point to another.

"They were not organized in cities," Heckenberger said. "There was a different pattern of small settlements, but they were all tightly integrated.

He said the population in one village and town complex was 2,500 to 5,000 people, but that could be just one of many complexes in the Amazon region.

"All the roads were positioned according to the same angles, and they formed a grid throughout the region," he said. Only a small part of these roads has been uncovered ,and it is uncertain how far the roads extend, but the area studied by his group is a grid 15 miles by 15 miles, he said.

Heckenberger said the people did not build with stone, as did the Mayas, but made tools and other equipment of wood and bone. Such materials quickly deteriorate in the tropical forest, unlike stone structures. Building stones were not readily available along the Amazon, he said.

Diseases such as smallpox and measles, brought by European explorers, are thought to have wiped out most of the population along the Amazon, he said. By the time scientists began studying the indigenous people, the population was sparse. As a result, some researchers assumed that was the way it was prior to Columbus.

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