History

The Chankillo site was built around 250 BC by the Casma-Sechín culture, one of the early complex societies of the Peruvian coastal desert. For decades after its discovery by archaeologists, the thirteen towers were interpreted as a fortification wall. The site’s astronomical function was identified only in 2007, when Ivan Ghezzi of Peru’s National Institute of Culture and Clive Ruggles of the University of Leicester published a landmark paper in Science demonstrating that the towers were a precisely engineered solar calendar instrument. Observed from two flanking posts to the east and west of the tower ridge, the movement of the sunrise and sunset along the horizon across the full year maps exactly onto the progression from the southernmost tower (summer solstice) to the northernmost (winter solstice). The thirteen towers divide this arc into approximately equal angular intervals of two to three degrees, enabling predictions of solstices, equinoxes, and agricultural calendar events to an accuracy of two or three days.

The ability to predict the solar calendar with such precision was almost certainly a power concentrated in the hands of the religious and political elite. The observatory is integrated into a larger ceremonial complex including a fortified compound with thick adobe walls and restricted internal corridors — suggesting that astronomical observations were conducted as part of controlled ritual practice. The site fell out of use after the Casma-Sechín culture declined, and its astronomical purpose was entirely forgotten until 2007. Following a decade of further excavation and research, Chankillo was inscribed on the UNESCO World Heritage List in 2021.