Ancient Humans Built Observatory in Desert 2,300 Years Ago That Tells Exact Date Using Sun—But How?

A 2,300-year-old solar observatory tells the date like a calendar using the sun. Janine Costa/AFP via Getty Images

In the beginning, there were the roaming alpacas, the bountiful green valleys that wound on forever, and the rising of a sun that was worshipped as a god.

When the Incas arrived at the Casma River Valley where a stone observatory once measured the passing of time using the sun, it must have seemed miraculous.