One thousand years before Columbus, there were pyramid builders, warriors -- the architects of an empire in South America. The Tiwanaku(蒂瓦纳科人) lived in a valley of Lake Titicaca（的的喀喀湖） for 1,500 hundred years. And then their civilization vanished,leaving behind only stone ruins and the enduring mystery of their passing.

 

The centerpiece of Tiwanaku's spiritual power was the Akapana Pyramid. Surrounding the pyramid, cities and temples, was a vast maze of channels and ridges.

 

Though they look like irrigation ditches, they were far too complex.

 

The mystery of their purpose is one that archaeologist Alan Kolata had been struggling to solve. Kolata had a hunch(预感), and to prove it he asked the local farmer to plant crops along the channel banks. Then the archaeologist and the farmers let in the water. Crops sprouted and began to grow. But then a tremendous frost hit the Altiplano.It devastated other fields, but the crops planted along the canals were not affected.

 

“The key to the sophistication of these, uh, of these raised fields system are really these canals that you see here all around me. What's important about the them is they function like gigantic solar collectors. If you flap this water you'll see that it's warm enough to bathe in,and it's truly remarkable and here we are up at 14,000 feet. And that's really the key to the system. It really prevents frost from damaging the crops that would be growing up on these field platform surfaces here.”

 

The mystery was solved.The Tiwanaku had found a way to control the environment of the valley itself. Their canals stored heat during the day then radiated it over the fields at night. This remarkable system provided the wealth to build an empire, and to keep it for over a millennium. But then amid growing political turmoil, the empire began to decline. For the Tiwanaku, it was the end, but for the local farmers, it is a new beginning. Secured from the frost, the raised fields proved to be seven times more productive, providing hope for a better harvest, and pride for their ancestors’ wisdom that is returned from the past.