A grouping of 127 granite blocks along a grassy Amazon hilltop may be the vestiges of South America's oldest astronomical observatory, according to archeologists who say the find challenges long-held assumptions about the region's prehistory. Farmers and fishermen in the region have known about this site for years, but archeologists only became aware of it thanks to a geological survey carried out in the region earlier in 2005. Credit: AP Photo/Gilmar Nascimento