Ruins predating the arrival of Europeans have been found in the Amazon near Calcoene, which is 390 kilometres (or 240 miles) from the city of Macapa, near the Brazilian border with French Guiana.
The ruins feature a temple once used as an observatory and which is reminiscent of Stonehenge, with evenly spaced blocks of granite arranged upright in circles. The blocks, which number 127, are three meters high (10 feet).
The observatory is believed to be up to 2,000 years old and located in an open space, with the blocks positioned to mark the winter solstice.
It is believed that in the time before Columbus, the forests of South America were home to millions of people. Knowledge of astronomy would seem to indicate an advanced civilisation in the Amazon.
Further reading: Amazon Stonehenge Suggests Advanced Ancient Rainforest Culture, Rhett Butler.