A Calendar of Towers
In the coastal desert of Peru's Casma Valley, a line of 13 stone towers sits on a 300-meter-long ridge. This arrangement is the Chankillo Archaeoastronomical Complex, built between 250 and 200 BCE. The entire site functions as a complete solar calendar, and it is considered the earliest known astronomical observatory in the Americas. The culture that constructed it, known as the Casma-Sechin, left behind a precise instrument for tracking the entire year.
The observatory works from two distinct observation points, one to the east and one to the west of the towers. From the western observation point, an observer can watch the sunrise against the "toothed" horizon created by the towers. As the year progresses, the position of the sunrise shifts along the line of towers. The June solstice sunrise aligns with the northernmost tower, and the December solstice sunrise aligns with the southernmost. The equinoxes occur between the sixth and seventh towers. By tracking the sun's daily movement from one tower to the next, the inhabitants could determine the date with an accuracy of one to two days. This dual-observation-point design, tracking both sunrise and sunset across the full solar arc, is unique among ancient observatory sites worldwide.
The towers themselves are made of stone and mortar and vary in height from 2 to 6 meters. Archaeological evidence suggests they were originally plastered and painted in shades of yellow, ochre, and white. The entire complex spans about four square kilometers and includes other structures for ceremonial and administrative purposes.
The Fortified Temple
On a nearby hilltop stands a large, triple-walled complex known as the Fortified Temple. Built with high walls and restricted gateways, some of which are false entrances, this structure was designed for defense. Radiocarbon dating places its construction in the same period as the observatory, between the mid-fourth century BCE and the early first century CE. The temple's placement suggests it was part of the same ceremonial center.
Research indicates that the society that built Chankillo existed during a period of conflict after the collapse of the older Chavín culture. The temple and observatory were likely used for sun worship rituals, possibly controlled by a warrior elite who used their command of the calendar to legitimize their power. Evidence of such rituals includes a large ceremonial vessel found at the observatory's entrance, decorated with clay figures of warriors in ritual combat. For unknown reasons, the entire complex was abandoned around the first century CE.