An ancient civilisation was flourishing in Peru over 5,000 years ago, making it the oldest known complex society in the Americas, Nature magazine has reported.
The civilisation had large ceremonial structures and agriculture
Archaeologists used radiocarbon dating to chart the rise and fall of the little known culture, which reigned over three valleys north of Lima.
The society, whose heyday ran from 3000 to 1800BC, built ceremonial pyramids and complex irrigation systems.
The find casts doubt on the idea that Andean civilisation began by the sea.
"The scale and sophistication of these sites is unheard of anywhere in the New World at this time," said Jonathan Haas, MacArthur Curator of Anthropology at the Field Museum, Chicago.
"The cultural pattern that emerged in this small area in the third millennium BC later established a foundation for 4,000 years of cultural florescence in other parts of the Andes."
The civilisation, which was characterised by stone pyramids, large ceremonial structures and agriculture, spread over three windy valleys in the Norte Chico region of Peru.
There were about 20 separate residential centres, which seemed to compete with each other to produce the most imposing architecture - some creating buildings as high as 26m (85ft).
The settlements spread over three windy and bleak valleys in the Norte Chico region of Peru
There is also some evidence of organised religion, the researchers say.
"They probably did have organised religion," said co-author Winifred Creamer, a Northern Illinois University (NIU) anthropologist. "Objects have been yielded which do point to religion, like anthropomorphic figurines."
The ancient society had a close inter-dependent relationship with nearby coastal settlements, which were uncovered much earlier by archaeologists.
The people of the inland Norte Chico area grew cotton, which they traded with their coastal neighbours in exchange for fish. In turn, the coast dwellers used the cotton to make their fishing nets.
Archaeologists have long known about the settlements on the coast in Peru. They were simple fishing communities and academics thought they represented the first civilisation in South America.
But carbon dating proves the inland sites of Norte Chico were just as old as the coastal dwellings, forcing experts to reassess the idea that all early civilisations were based by the sea.
"In Norte Chico, the path of cultural evolution in the Andean region diverged from a relatively simple hunting and gathering society to a much more complex pattern of social and political organisation," said Alvaro Ruiz, of NIU.
Professor Creamer is glad she got to explore these sites before they were buried by modern farms
"With this new information, we need to rethink our ideas about the economic, social and cultural development of the beginnings of civilisation in Peru and all of South America."
After 1800 BC, when the settlements were abandoned, it is likely that the Norte Chico people moved to other parts of Peru, taking their innovations and culture with them.
"One very likely scenario is that they took their irrigation further north and further south to areas that were more productive," said Professor Creamer.
"It is interesting that in the Casma valley, which is directly north, there are even bigger pyramids, and that was the next major cultural event."
Question of qualification
Professor Creamer believes it is possible that other major Andean cultures, like the Chavin civilisation, which thrived about 3,000 years ago, may have descended from the Norte Chico people, or been culturally influenced by them.
However, there is still some discussion as to whether the Norte Chico society actually qualified as a "civilisation" itself.
Different anthropologists have different definitions of the word, and the Norte Chico people fell outside some of them.
"Some people would say they were not a civilisation," said Professor Creamer. "They had very few arts and crafts for example - they were pre-ceramic.
Other civilisations may have descended from the Norte Chico people
"And if civilisation needs urbanisation - well, we don't know if these sites qualify as urban centres yet."
Whatever the definition of civilisation, Professor Creamer and her team are just glad archaeologists discovered these historic sites before they got destroyed by modern agriculture.
"Peru has laws to protect sites like this one, but they don't always work," she said. "We are very lucky we got to explore these sites before they were buried under drip irrigation or chicken farms."