A study based on over 20 years of research into an ancient site in the Amazon rainforest has revealed evidence it was once a large-scale hub of interconnected cities that date back more than 2,500 years. The findings were published Thursday in the journal Science and detail the researchers’ work in mapping the network of settlements, which may be the earliest example of urbanism ever documented in the Amazon. “It was a lost valley of cities,” said Stéphen Rostain, first author of the study and a director of France’s National Center for Scientific Research.