Deforestation of the Amazon basin as thrown up one unexpected plus. Signs of what could be a previously unknown ancient civilisation are emerging from beneath the felled trees of the Amazon. Some 260 giant avenues, ditches and enclosures have been spotted from the air in a region straddling Brazil's border with Bolivia. The geoglyphs are formed by ditches up to 11 metres wide and 1 to 2 metres deep. They range from 90 to 300 metres in diameter and are thought to date from around 2000 years ago up to the 13th century. Excavations have unearthed ceramics, grinding stones and other signs of human habitation at some of the sites but not at others. This suggests that some had purely ceremonial roles, while others may also have been used for defence.

The traditional view is that before the arrival of the Spanish and Portuguese in the 15th century there were no complex societies in the Amazon basin – in contrast to the Andes further west where the Incas built their cities. Now deforestation, increased air travel and satellite imagery are telling a different story.