The old wall may have been built to protect against El Niño flooding

Known as Muralla La Cumbre, this wall was once believed to have protected important farmland from invaders. But new research suggests it actually prevented El Niño flooding from wreaking havoc.

The ancient earth wall is about 10 kilometers long and is located in the desert near Trujillo in northern Peru. It was built near the former capital of Chan Chan. This city belonged to the Chimú people (also known as the Kingdom of Chimor) who lived on the coast of northern Peru from around the 9th centuryth Until the 15thth century AD

Many of us have heard of the various pre-Columbian peoples of South and Central America, such as the Maya, the Incas and the Aztecs, but the Chimú are often overlooked.

In its day, this civilization was the largest and most prosperous culture in the region, occupying 1,000 kilometers of coastline that extended into what is now northern Chile. Despite their importance, the Chimú were eventually conquered by the Incas, with whom they had long been enemies.

Until recently it was believed that Muralla La Cumbre was built as a result of these hostilities. It was thought to have served as a barrier to protect the Chimú from invasion.

“According to several accounts written in the colonial period, the descendants of the Inca and Chimú nobles told the Spanish that both the Incas and the Chimú fought a long war between 1400 and 1450 AD,” Gabriel Prieto, Assistant Professor in the Department of Anthropology at the University of Florida told IFLScience. “The wall [near] Chan Chan is then considered part of the defensive strategy to protect against Inca raids.”

However, Prieto has found evidence that Muralla La Cumbre did in fact protect the area from the devastating floods that occurred during Peru’s wettest periods, known as El Niño.

An El Niño occurs when sea temperatures in the tropical eastern Pacific rise 0.5°C (0.9°F) above normal, leading to warmer-than-average weather. These effects typically occur every few years, peaking in December. The term means “the boy” and is believed to derive from “El Niño de Navidad” several centuries ago, when Peruvian fishermen described the weather in allusion to the newborn Christ at Christmas.

El Niño brings drought in some parts of the world, but heavy rains fall in Ecuador and northern Peru. These waters have historically posed a significant threat to local populations, particularly the Chimú.

During his research on Muralla La Cumbre, Prieto found layers of floodplain sediment on one side of the wall, the east side, suggesting it was built to protect farmland to the west.

“I tested an old hypothesis put forward in 2003 by two Peruvian archaeologists: Victor Piminchumo and César Gálvez,” Prieto told IFLScience. “In 2021 I got funds to dig it by selecting a section of the wall that crosses one of the dry canyons and I was very lucky to find the sediments on the east side.”

Photo of the excavation site showing the layers of floodwater sediment in the ground

El Niño left clear traces of floodplain sediment on the east side of the old wall.

Credit: Gabriel Prieto/Huanchaco Archaeological Project

According to radiocarbon dating results, the lower parts of the wall may have been built around 1100 AD as a result of El Niño floods.

Prieto’s analysis also found that one of the layers of sediment dates from around 1450, consistent with evidence of a mass sacrifice of about 140 children and 200 llamas elsewhere in Chimú. To Prieto, this could be a sign that the Chimú knew the dangers of El Niño floods, which prompted their rulers to make sacrifices to appease their gods.

This research is important on several levels, Prieto told IFLScience. “It shows that the Chimú not only pleased their gods with human and animal sacrifices, but also created technical and effective infrastructures to deal with the ill effects [El Niño]. They also built a kind of dam that held back the sediments and rich silts that might have been used to fertilize agricultural fields.”

It appears that the Chimú were much more advanced in terms of their technologies than is often assumed, particularly in relation to their “hydraulic infrastructure” that helped them deal with strong climate anomalies such as those caused by El Niño. As a result, “modern nations like Peru still suffer because they don’t pay enough attention to simple technologies with effective outcomes,” Prieto added.

An article on Prieto’s research has been accepted for publication and will be published soon.

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