New? Old? Did ancient Amazonians build a 'Stonehenge'?

A grouping of granite blocks along a grassy Amazon hilltop may be the vestiges of a centuries-old astronomical observatory -- a find archaeologists say indicates early rain forest inhabitants were more sophisticated than previously believed.

The 127 blocks, some as high as 9 feet, are spaced at regular intervals around the hill, like a crown 100 feet in diameter.

On the shortest day of the year -- December 21 -- the shadow of one of the blocks disappears when the sun is directly above it.