A Peruvian site previously reported as the oldest city in the Americas is actually part of a large cluster of as many as 20 cities with massive pyramids and sunken, circular plazas sprawled over three river valleys, researchers report today.
Construction started about 5,000 years ago -- nearly 400 years before the first pyramid was built in Egypt -- at a time when most people throughout the world were hunters and gatherers, a team from Northern Illinois University and Chicago's Field Museum reports in today's issue of the journal Nature.
The society -- its people are referred to by no name other than "Andeans" -- persisted in virtually the same form for 1,200 years before being overrun by more warlike neighbors. That is the longest any ancient civilization is known to have survived, said archeologist Jonathan Haas of the Field Museum, who led the expedition.
The new results greatly expand understanding of how complex states began in the Americas.
"We are seeing the emergence of centralized decision making, government and religion out of pristine conditions," Haas said. "They were not following a pattern established by someone else. They were developing it on their own. An Andean culture was being invented in this area."
Haas said that it had long been thought that the Americas were behind Europe, Africa and Asia in developing civilizations. The new dates for the region show that the Americas, separated from the other centers of civilization by then-impassable oceans, developed more or less simultaneously.
The findings are also overturning the belief that South American civilization was based in coastal cities supported by fishing. Instead, Andean society seems to have been built mainly on cotton farming and trade with fishing villages along the coast of what is now Peru.
"It's a unique system," Haas said. "There wasn't anything like this in the world as far as I can tell."
The first city of the complex to be discovered, Caral, is in the Supe River valley, about 90 miles north of Lima, the Peruvian capital. It was virtually ignored for more than 100 years after its discovery, despite the presence of nearly 100-foot-tall pyramids. It had no golden or jeweled artifacts, no pottery shards with which to date it, and no art or writing to indicate its ancient origins.
It was not until Haas' team first reported radiocarbon dating results for the site three years ago that scientists appreciated its antiquity. Those findings indicated that Caral was built about 2600 BC, much earlier than researchers had thought possible.
New dates from the Supe Valley and nearby Pativilca and Fortaleza valleys show that construction began there even earlier, about 3000 BC, and spread over more than 700 square miles.
The driving force for this society may well have been the Humboldt Current, a broad band of cold water that sweeps north from Antarctica along the Peruvian coast. The current is rich in marine life, which served as a valuable food source for the first settlers, researchers say.
But about 3100 BC, the climate turned drier, eliminating the naturally growing fruits and vegetables with which villagers supplemented their diet of fish. Over a period of about 100 years, Haas said, they began looking inland for new food sources.
"They figured out that if you take water out of the rivers and put it on desert land, the desert blooms and becomes very productive," he said. In the three valleys of the Norte Chico region, they could do so by hand-digging short canals.
"In any other valleys, canal systems tend to be much more complex," he said. "Irrigation is easier here than anywhere else."
They grew guava, beans, peppers and fruits -- but not the corn or potatoes that researchers previously believed necessary to support a large population.
But their most important crop was cotton, which was traded to the coastal villagers, who used it to make fishing nets. "You can't catch anchovies without nets," Haas said. Anchovies were the Andeans' primary food.
The Andeans had a very peaceful society. "They didn't fight with each other, and nobody else was big enough to fight with them," Haas said.
Evidence indicates that the fishermen were making seasonal inland visits to participate in ceremonial activities and perhaps to help build monuments.
"We see temporary populations, building very ephemeral houses. We see signs of feasting -- large communal hearths, food materials and garbage incorporated into the mounds," he said.
But beginning about 1800 BC, possibly because the soil began to lose its productivity, new buildings and monuments got smaller and the big cities began to decline. About the same time, new, larger cities began to grow north and south of Norte Chico as some of the people took their knowledge of canal building and sought more fertile soil.
Eventually, warfare began, and Norte Chico was conquered and abandoned. Today, the only occupants are scattered farmers.