Stone towers make up oldest observatory in Peru

By Maggie Fox, Health and Science Editor

WASHINGTON (Reuters) - A line of 13 stone towers that top a coastal hillside in Peru are in fact the Western Hemisphere's oldest solar observatory, researchers said on Thursday.

The 2,300-year-old site points to a sophisticated culture that used the dramatic alignment of the sun and the structures for political and ceremonial effects, the researchers said.

The site, called the Thirteen Towers of Chankillo, precisely spans the annual rising and setting arcs of the sun when viewed from two specially constructed observation points.

"Thousands of people could have gathered to watch impressive solar events. These events could have been manipulated for a political agenda," said Ivan Ghezzi, who made the discovery while a graduate student at Yale University and who is now archeological director of the Instituto Nacional de Cultura (National Institute for Culture) in Peru.

For instance, at the time of the summer solstice in June, the longest day of the year, the sun rises just to the left of the northernmost tower, Ghezzi said in a telephone interview.

Chankillo is a large ceremonial center laid out over several square miles (kilometers). It has a heavily fortified hilltop structure, thick walls and parapets. But no one quite understood a 300-yard-long (meter-long) line of towers that sits on a nearby hill like spines on a dragon's back.

Writing in the journal Science, Ghezzi and colleagues said they figured it out.

"Since the 19th century there was speculation that the 13-tower array could be lunar demarcation -- but no one followed up on it," Ghezzi said. He tested the idea while studying military structures at the site, which dates to the fourth century BC.

"We were there. We had extraordinary support from the Peruvian government, Earthwatch and Yale University. We said, 'Let's study it while we are here.'"

SEEKING VERIFICATION

But it took him several years to contact Clive Ruggles, a leading British authority on archeoastronomy, for verification.

"In the five-hour drive to the towers I could see that he was a little skeptical," Ghezzi said. "When he got there and made a few measurements he realized that from the points we were showing him, the alignments worked out perfectly."

Ruggles, of the University of Leicester, said often such claims do not pan out. But this one did.

"The fact that, as seen from these two points, the towers just span the solar rising and setting arcs provides the clearest possible indication that they were built specifically to facilitate sunrise and sunset observations throughout the seasonal year," he said in a statement.

Ghezzi said little is known of the people who built Chankillo. They pre-date the Incas by centuries.