The Earliest-Known Astronomical Observatory in the Americas May Offer New Insights

There was a time when Stonehenge was believed to be a kind of “Neolithic computer.” Archaeology has since corrected that misconception. Today, the evidence points strongly in another direction: to an arid hill in the Casma Valley on Peru’s northern coast, about 200 miles north of Lima.

There stands Chankillo, a complex built around 250 B.C.E., considered the earliest known solar observatory in the Americas and the clearest known example of a monument designed to track the sun’s position throughout the entire year, according to a study in Science. Modest in appearance and largely absent from tourist posters and classic postcards, Chankillo has renewed attention as archaeologists report preliminary findings from ongoing excavations.

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Understanding the Chankillo Site

Researchers working at the site, designated a UNESCO World Heritage Site in 2021, have reported preliminary evidence of a structure that may predate the Chankillo solar observatory. Based on its orientation, stratigraphy, and construction techniques, archaeologists suggest that this building could reflect earlier forms of astronomical knowledge at the site. These findings have not been peer-reviewed.

“It doesn’t function as a sundial because it doesn’t measure the hours of the day. It’s a monumental solar calendar,” says archaeologist Iván Ghezzi, director of the Chankillo Executing Unit within Peru’s Ministry of Culture.

He adds, “Other sites allow us to mark solstices, equinoxes, or perhaps an important lunar position. Chankillo, by contrast, functions every single day of the year. It is a complete solar calendar, and the only one of its kind in the world.”

Chankillo Is More Than a Solar Observatory

The archaeological complex represents one of the most monumental expressions of Casma-Sechín culture tradition, among the oldest and most enigmatic in northern Peru, known for its stone sculptures depicting violent ritual scenes. During this period, the sun played a central ritual and symbolic role in many Andean societies. The site lies within a vast territory — approximately 965 square miles — shaped by both natural and cultural forces, encompassing ceremonial, administrative, residential, and defensive areas.

“The challenge of interpreting Chankillo has always been to reconcile the buildings that speak of warfare with those that speak of astronomy,” says Ghezzi.

At the heart of the complex are the famous 13 towers, several carefully arranged observation points, and an imposing Fortified Temple that dominates the landscape.

The towers, ranging from roughly 10 feet to 23 feet in height, form a jagged horizon nearly 1,000 feet long. Observed from specific vantage points, they track the sun’s rising position across the entire year. During the December solstice, the sun appears beyond one end of the alignment; six months later, at the June solstice, it rises at the opposite end. Between these two extremes, the sun’s daily movement can be registered with remarkable accuracy.

Ghezzi recalls the day he grasped how the system worked, compass in hand: “It was one of the most remarkable days of my life. Every morning before beginning the excavations, we went to watch the sunrise, and sure enough, the towers aligned with the sun’s arc. It was a true eureka moment.”

From Solar Observatory to Astronomical Observatory

Beneath the currently visible observatory, preliminary field reports describe older structures with distinct construction techniques that may predate the construction of Chankillo. Although radiocarbon dates are still pending and formal publication, these features could reflect earlier evidence of sky-watching at the site.

The findings also extend beyond the sun. Researchers noted a corridor that may align with a position in the moon’s long-term cycle, sometimes known as the major lunistice.

Based on this evidence, Ghezzi has moved away from referring to the complex as a “solar observatory” and instead calls it, more accurately, the astronomical observatory of Chankillo.

A Symbol of War and Stars

Among the recent discoveries, one stands out for offering an unexpected interpretive key to the observatory’s use: a ceramic vessel, decorated with figures of warriors in combat, found in fragments but reconstructable within an area of the Chankillo complex.

According to Ghezzi, it was not a utilitarian object but a symbolic marker, possibly linked to ceremonies.

“Its placement in a restricted-access area of the observatory points to the existence of elites who combined astronomical knowledge with military leadership, reinforcing the political and ritual role of the Fortified Temple,” the archaeologist explains.

The vessel appears to provide the first material link between these two worlds. The depictions include warriors seemingly defending a building, likely the Fortified Temple itself, which suggests an elite with military leadership and high social status.

“This indicates that these individuals, warriors and leaders, were associated not only with military power but also with astronomical knowledge,” Ghezzi concludes.

United Under the Same Sky

Despite being roughly 2,300 years old, Chankillo remains an exceptional case of standing architecture. Atmospheric conditions along Peru’s coast have favored the preservation of its structures: walls partially collapsed but still visible, neither buried nor completely destroyed by time.

The main threat comes from extreme climate events. Along Peru’s coast, El Niño can bring intense rainfall that can severely damage archaeological remains. Although Chankillo lies farther south than the most vulnerable areas near the Ecuadorian border, the risk remains non-negligible.

For now, Chankillo is not officially open to the public. Even so, the site already receives daily visitors. A preliminary route allows visitors to explore part of the complex and observe this “wonder of world heritage,” while the team proceeds to a critical phase: conservation.

Within the coming years, Peru’s Ministry of Culture expects to formally open at least the most important sector of the complex — the Astronomical Observatory. By then, the project will include not only the protection of the structures but also visitor routes, parking areas, and public information spaces.

And so, as Chankillo’s walls continue to mark the passage of the sun and the moon, the earliest-known observatory in the Americas prepares to become, once again, what it was from the very beginning: a place where the sky and human life were understood as the same.

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