Known. Laser maps showed mounds, plazas, and roads under the Amazon forest.
The sites are in the Upano Valley, in Ecuador. People used them from about 500 BC to between AD 300 and 600. More than 6,000 earth mounds held homes and ceremonial buildings. Roads as wide as 10 metres ran for 10 to 20 kilometres and linked the centres. Fields and drainage canals lay around them. The lead researcher says this is older than any other site known in the Amazon.
How many people lived there is still a guess, from at least 10,000 to perhaps 15,000 or 30,000.
https://www.ancient-origins.net/news-history-archaeology/oldest-amazonia-settlement-ecuador-0020200