Did the early indigenous peoples of the rainforest look to the stars to measure time and mark the passage of the seasons? Archaeologists believe they did.
This photograph shows what is being called the tropical Stonehenge, a grouping of 127 granite blocks, each 10ft high and spaced at regular intervals around a grassy hilltop in northern Brazil. On the winter solstice, 21 December, the shadow of one of the blocks disappears, leading experts to believe the formation was used as a calendar.
"Only a society with a complex culture could have built such a monument," said Mariana Petry Cabral, of the Amapa Institute of Scientific and Technological Research.
The blocks are located near the village of Calcoene, in Amapa state, close to the border with French Guiana. Ms Cabral believes that the site was once inhabited by the Palikur Indians and says pottery discovered there may be more than 2,000 years old.
Michael Heckenberger, an anthropologist at the University of Florida, said it was a novel find. "The traditional image is that some time thousands of years ago small groups of tropical forest horticulturists arrived in the area and they never changed - [that] what we see today is just like it was 3,000 years ago."Reuse content