The Thirteen Towers: Peruvian Citadel is Site of Earliest Ancient Solar Observatory in the Americas

The Thirteen Towers of Chankillo have been discovered to span, almost exactly, the annual rising and setting arcs of the sun when viewed from two specially constructed observation points.

The existence of this observatory predates the European conquests by 1,800 years and even precedes the monuments of similar purpose constructed by the Mayans in Central America.

Chankillo is a large ceremonial centre covering several square kilometers. It was better known in the past for a heavily fortified hilltop structure with massive walls, restricted gates, and parapets. But the purpose of a 300m-long line of Thirteen Towers lying along a small hill nearby had remained a mystery. New evidence now identifies it as a solar observatory.

And the researchers go further-pointing to evidence of an ancient Sun cult participating in public rituals and feasts directly linked to the observation and interpretation of the seasonal passage of the Sun.

They claim Sun worship and related cosmological beliefs could have helped to legitimize the authority of an elite class – two millennia before the Incas.

The research was carried out by Ivan Ghezzi, a graduate student in the Department of Anthropology at Yale University who is now Archaeological Director of the Instituto Nacional de Cultura (National Institute for Culture) in Peru, and Professor Clive Ruggles, of the School of Archaeology and Ancient History at the University of Leicester. Professor Ruggles is one of the world’s leading authorities on archaeoastronomy.

Recorded accounts from as early as the 16th century A.D. detail practices of state-regulated sun worship during Inca times, and related social and cosmological beliefs. These speak of towers being used to mark the rising or setting position of the sun at certain times in the year, but no trace of the towers remained. At Chankillo, not only were there towers marking the sun’s position throughout the year, but they remain in place, and the site was constructed much earlier – in approximately the 4th century B.C.

“Archaeological research in Peru is constantly pushing back the origins of civilization of the Americas in the Andean area. In this case, the 2,300 year old solar observatory at Chankillo is the earliest such structure identified and unlike all other sites contains alignments that cover the entire solar year,” said Dr Ghezzi.

Chankillo is situated in the costal Peruvian desert. From the observing points, the thirteen towers are strikingly visible on the horizon, resembling large prehistoric teeth. Around the observing points are spaces where artifacts indicate that ritual gatherings were held.

For many years, there has been a controversy as to whether Chankillo was a fort or a ceremonial centre. The current report offers strong evidence for an additional use — as a solar observatory and a fortified temple.

Carbon-dated by the researchers, the monument at Chankillo was constructed in the same time period as other “Wonders of the Ancient World.” It is remarkable as the earliest known complete solar observatory in the Americas that defines all the major aspects of the solar year.

Ghezzi was originally working at the site as a Yale graduate student conducting thesis work on ancient warfare in the region, with a focus on the fortress at the site.

Noting the configuration of the 13 towers in 2001, Ghezzi wondered about a relation to the lunar year cycle. “Since the 19th century there was speculation that the 13-tower array could be lunar demarcation — but no one followed up on it. 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!’”

To his great surprise, within days they had measurements indicating that one tower aligned with the June solstice and another with the December solstice. But it was several years before Ghezzi connected with co-author Clive Ruggles, a leading British authority on archeoastronomy. Ruggles was immediately impressed with the monument structures.

“I am used to being disappointed when visiting places people claim to be ancient astronomical observatories.” said Ruggles. “Since everything must point somewhere and there are a great many promising astronomical targets, the evidence — when you look at it objectively — turns out all too often to be completely unconvincing.”

“Chankillo, on the other hand, provided a complete set of horizon markers — the Thirteen Towers — and two unique and indisputable observation points,” Ruggles said. “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.”

What they found at Chankillo was much more than the archival records had indicated. “Chankillo reflects well-developed astronomical principles, which suggests the original forms of astronomy must be quite older,” said Ghezzi.

The researchers also knew that Inca cultural practices in much later times were intimately linked to the political operations of the Inca king, who considered himself an offspring of the sun. Finding this observatory revealed a much older precursor where calendrical observances may well have helped to support the social and political hierarchy. They suggest that this is the first unequivocal evidence, not only in the Andes but in all the Americas, of a monument built to track the movement of the sun throughout the year.

According to the authors, monuments are statements about how a society is organized; about who has power, and who does not. The people who controlled these monuments “controlled” the movement of the sun. The authors pose that this knowledge could have been translated into the very powerful political and ideological statement, “See, I control the sun!”

Chankillo is one of the most exciting archaeoastronomical sites I have come across,” said Ruggles. “It seems extraordinary that an ancient astronomical device as clear as this could have remained undiscovered for so long.”

Support for the project came from Yale University, the Pontificia Universidad Católica del Peru, the National Science Foundation, the Wenner-Gren Foundation, the Field Museum, the Schwerin Foundation, Earthwatch Institute and the Asociación Cultural Peruano Británica (Anglo-Peruvian Cultural Association) in Lima, Peru.

Citation: Science (March 2, 2007)