Sao Paulo - Brazilian archaeologist Denise Schaan still does not believe in the legendary land El Dorado, although she and her team keep finding signs of an ancient and advanced civilization in the western Amazon basin. The signs point to a people that lived there more than a millennium ago in systematically built settlements with a sophisticated road network.

With the aid of satellite imagery and photographs taken from airplanes, the archaeologists have so far identified more than 260 geoglyphs, or large geometric figures carved in the ground. The figures have been laid bare by increasing deforestation of the long-impenetrable jungle.

'Up to now it's been nearly impossible to see the geoglyphs because they were covered by the dense rain forest,' Schaan, a professor at the Federal University of Para in Belem, Brazil, told the German Press Agency dpa.

Alceu Ranzi, a countryman and now Schaan's colleague, spotted the geoglyphs and quickly realized that the lines forming circles and rectangles, between 100 and 300 metres in diameter, must be man-made. He made his first discoveries in the late 1990s near the Bolivian border. Schaan and a Finnish archaeologist joined the search in 2005, and the three began evaluating aerial photographs.

First Ranzi took photographs from a plane. Then the researchers systematically analyzed pictures from Google Earth. Once they had gone through all those images, the Brazilian government made available satellite photographs taken to document and monitor the progressive destruction of the Brazilian rain forest.

Discernible in the photographs were ditches that had been excavated long ago. Earthen walls alongside them, up to a metre high, were difficult to make out, however. The researchers are sure that the geoglyphs, spread over a 250-kilometre-wide area in the Brazilian state of Acre, indicate a former civilization.

The ditches have been laid out in a systematic way. Many earthen avenues lead directly to rivers. 'What's more, a lot of the ditches are similar in size and about 11 to 11.5 metres wide,' Schaan said. 'We presume they were created by Arawak Indians.'

The civilization must have comprised tens of thousands of people. Schaan estimates that the geoglyphs date from sometime between 200 AD and the end of the 13th century. 'But I don't think they've got anything to do with El Dorado,' she said.

Many hundreds of years later, the Spanish conquistadors believed that this legendary land, rich in gold and precious stones, existed somewhere in South America. Thousands of adventurers came to look for it too, but most only met their deaths.

The search for a lost civilization was also behind repeated expeditions into the Brazilian jungle by British explorer Colonel Percy Harrison Fawcett in the early 20th century. Fawcett had been told of the existence of a vanished city, which he named 'Z.' In 1925, he himself disappeared without a trace in the jungle.

A feature film about Fawcett is currently in the works. Called 'The Lost City of Z,' it will star the American actor Brad Pitt.

Perhaps the team of archaeologists led by Ranzi and Schaan will find answers to some of Fawcett's burning questions. Schaan believes only a fraction of the geoglyphs have been discovered so far and that there are probably at least 1,000 more.

'Similar figures certainly exist in areas we haven't searched at all,' she said.

The Brazilian researchers still have plenty of questions of their own. What exactly do the circles and rectangles mean? What were they used for? Do they also have symbolic significance? What was the vegetation like at the time? Was the area covered with rainforest or was it possibly a savannah?

To help answer these questions, the scientists plan to uncover some of the geoglyphs still under the forest canopy in the hope they are better preserved. Perhaps, after centuries, the Amazon basin will finally reveal whether all those adventurers were simply hunting a myth. Or maybe there really is some truth to the legends of a lost city, be it El Dorado or 'Z.'