HUNDREDS of geometric monuments unearthed deep in the Amazon may have been left behind by a previously unknown society, say scientists.
Archaeologists have found more than 200 earthworks shaped as perfect circles and squares, many connected by straight roads.
They have dated one site to 1283AD but say others could be from as early as 200AD.
The earthen foundations were found in a region more than 150miles across, covering northern Bolivia and Brazils Amazonas state.
The first ones were uncovered in 1999, after large areas of pristine forest was cleared for cattle grazing.
Sculpted from the clay rich soils of Amazonia, the earthworks are made up of 30ft wide and 10ft deep ditches alongside 3ft high walls.
The largest ring ditches founds so far are 1,000ft in diameter.
The earthen structures or 'geoglyphs can now be spotted against the treeless, savanna-like landscape and scientists have compiled an archive using Google Earth.
A team of researchers have analysed all the findings in a paper published in the journal Antiquity.
They found that most earthworks were clustered on a 200m high plateau at the top of river valleys.
This would have given inhabitants a defensive advantage with a clear view of people coming up river.
Most were also placed near spring water sources.
The researchers hypothesised that the monuments may also have had a ceremonial function, due to the highly symbolic geometric shapes used.
Co-author Denise Schaan from Federal University of Par in Brazil, said: 'Whether the sites were purely ceremonial or defensive, it is clear that the area was densely populated by relatively sedentary people at the eve of European contact.
Daily Mail

This news was published in The Nation newspaper. Read complete newspaper of 07-Jan-2010 here.