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Mystery Towers in Peru Are an Ancient Solar Calendar

Science  02 Mar 2007:
Vol. 315, Issue 5816, pp. 1206a-1207a
DOI: 10.1126/science.315.5816.1206a

Since the 19th century, archaeologists have puzzled over Chankillo, a massive, 2300-year-old ruin 400 kilometers north of Lima, with a walled hilltop center and an enigmatic line of 13 small, rectilinear towers. Scientists have variously interpreted the complex “as a fort, a redoubt, a temple, and even as the setting for ceremonial battles,” says archaeologist Iván Ghezzi of the Pontificia Universidad Católica del Perú (PUCP) in Lima.

Now, on page 1239, Ghezzi and archaeoastronomer Clive Ruggles of the University of Leicester, U.K., demonstrate that Chankillo was, in part, a solar observatory. In what Luis Guillermo Lumbreras of the Universidad Nacional Mayor de San Marcos in Lima calls “an excellent scientific contribution, very serious and informative,” Ghezzi and Ruggles show that the sequence of towers marked the summer and winter solstices.

Jokingly dubbed “the Norelco ruin” for the distinctive shaverlike shape of its three concentric walls, Chankillo was built during the collapse of a major Andean relig;ious center called Chavín de Huántar, in a time when many population centers were emptied and others were fortified. Among the most visible of the latter is Chankillo, which was erected between 200 and 300 B.C.E. according to new radiocarbon dates also provided in the paper.

View from the top.

Chankillo's central complex was associated with a solar observatory.


Chankillo's commanding location and thick walls suggest a martial purpose, but its elegant design, many gates, and lack of water supply raise doubts that it was a fort. Working with Ruggles, Ghezzi uncovered two artificial observation points constructed about 200 meters away from and on opposite sides of the line of towers, which run along the top of a ridge east of the main complex. The eastern viewpoint was partly wrecked, but the western viewpoint was both well-preserved and, to Ghezzi and Ruggles, unambiguous in function: The two viewpoints are positioned so that on the winter and summer solstices the sun rises and sets over the towers on the opposite end of the line, establishing the beginning and midpoint of the solar year. The western viewpoint was at the end of a 40-meter-long, windowless corridor that wrapped around the outside wall of a structure filled with ceremonially displayed ceramic figurines of soldiers.

Because the heavens are filled with celestial objects, researchers often fool themselves with coincidental astronomical alignments. “When Iván said I had to come and see this site that might be an observatory,” Ruggles says, “inside I was thinking, ‘Yeah, yeah, yeah'—people are always saying this to me.” But instead, he found what PUCP archaeologist Luis Jaime Castillo calls an “absolutely clear-cut” example of a monumental calendar. “It is difficult to imagine what other function the observation structures could have served,” says Castillo.

The practical need for the Chankillo observatory is evident, notes Daniel Sandweiss of the University of Maine, Orono: agriculture, which required “solar observation to know when to plant.” Along the bone-dry Peruvian coast, where farming has long depended on irrigating rivers, “people need to know the date with some precision.”

Until recently, the first complex states in northern Peru were dated to the rise of the Moche in about 400 C.E. “Now we find very sophisticated measurement techniques 600 years before Moche,” says Castillo. “It says to us that there may have been more going on than we thought.”

Most important, says Clark Erickson of the University of Pennsylvania, “this kind of discovery really begins to get into the minds of people in the past.” The long hallway to the western observation point, he notes, “only provides space for a few people to be brought there and dazzled.” Understanding this piece of architectural theater, he says, “helps make the past come alive.”

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