Each settlement is organized around a central plaza and linked to others via precisely placed roads. In their heyday, some of the settlements were home to perhaps thousands of people and were about 150 acres (61 hectares) in size.
A major road aligned with the summer solstice intersects each central plaza.
The larger towns, placed at cardinal points from the central seat of power, were walled much like a medieval town, noted Heckenberger. Smaller villages and hamlets were less well defined.
Between the settlements, which today are almost completely overgrown, was a patchwork of agricultural fields for crops such as manioc along with dams and ponds likely used for fish farms.
"The whole landscape is almost like a latticework, the way it is gridded off," Heckenberger said. "The individual centers themselves are much less constructed. It is more patterned at the regional level."
At their height between A.D. 1250 and 1650, the clusters may have housed around 50,000 people, the scientists noted.
According to Heckenberger, the planned structure of these settlements is indicative of the regional planning and political organization that are hallmarks of urban society.
"These are far more planned at the regional level than your average medieval town," he said, noting that rural landscapes in medieval settlements were randomly oriented.
"Here things are oriented at the same angles and distances across the entire landscape."
The research "raises huge and important questions," Susan Hecht, an Amazon specialist at the University of California, Los Angeles, was quoted saying in a related Science news piece written by Charles Mann.
Mann is the author of the 2005 book 1491: New Revelations of the Americas Before Columbus, which describes theories of urban planning in the Amazon.
For one, Hecht was quoted as saying, the research adds further weight to the idea that the Amazon Basin once supported large and complex societies.
Other scientists, notably archaeologist Betty Meggers at the Smithsonian Institution in Washington, D.C., have argued that Amazonian soils were too poor to support large human populations for extended periods.
Hecht said the research also challenges the idea that urbanism means a central, dominant, and powerful city. Smaller, but highly connected settlements may also have been common.
According to study co-author Heckenberger, the clusters of towns in the pre-Columbian Amazon were similar to the system envisioned by British planner Ebenezer Howard in his 1902 book, Garden Cities of Tomorrow.
Howard argued for a system of tightly linked smaller cities instead of large megacities that are an eyesore on the natural world.
"If [he] knew about Xingu, it would have been a chapter in his book," Heckenberger said.
And now that the Amazonian "garden cities" have been found, Heckenberger added, scientists and planners ought to study them closely for alternatives to the modern system that is destroying vast reaches of the Amazon and displacing the last of the region's indigenous tribes.
"We know that we have to come up with alternatives," he said, "so here is a place we may want to look."
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