The Secret of El Dorado

In 1542, the Spanish Conquistador, Francisco de Orellana ventured along the Rio Negro, one of the Amazon Basin's great rivers. Hunting a hidden city of gold, his expedition found a network of farms, villages and even huge walled cities. At least that is what he told an eager audience on his return to Spain.

"No one ever saw again what Orellana described"
Dr James Petersen, University of Vermont
The prospect of gold drew others to explore the region, but none could find the people of whom the first Conquistadors had spoken. The missionaries who followed a century later reported finding just isolated tribes of hunter-gatherers. Orellana's story seemed to be no more than a fanciful myth.

A proven liar?
The search for clues in the Amazon takes place at grass roots level - in the soil itself. Along Brazil's Tapajos River, archaeologist Bill Woods has mapped numerous prehistoric sites, some with exquisite, 2,000 year old pottery. There is a common thread: the earth where people have lived is much darker than the rainforest soil nearby. Closer investigation showed that the two soils are the same, the dark loam is just a result of adding biological matter. The Brazilians call this fertile ground terra preta. It is renowned for its productivity and even sold by local people.

Archaeologists have surveyed the distribution of terra preta and found it correlates favourably with the places Orellana reported back in the 16th century.