Two large structures near the Red Pyramid in Egypt may be the remnants of an ancient dam, which would be one of the oldest major dams ever built. The work suggests a level of technical sophistication and control over water resources that wasn’t previously expected of the engineers of the earliest pyramids. 

The Red Pyramid was the second major pyramidal tomb project under the rule of the 4th-dynasty pharaoh Snefru, which lasted from around 2613 to 2589 BC. It is considered the first “true” pyramid with a consistent, smooth slope on all sides, setting the stage for its more famous counterparts that would later be built in Giza.

In 1843, researchers identified two large structures across the Wadi Dahshur valley, just 40 metres from the Red Pyramid. Since 1947, researchers have believed these structures were construction ramps or roads used to transport large limestone blocks from quarries to the pyramids. But emerging research about Egypt’s wetter past has led some scholars to question this longstanding hypothesis.

To further investigate the structures, Xavier Landreau at , a private research institute in France, and his colleagues used satellite imagery, historical maps, topographical modelling and watershed analysis. Their results clearly outlined the features and how they fit the surrounding landscape, showing they each measured around 600 to 700 m long, 15 to 30 m wide and 6 or 7 m tall, and are separated by about 200 m. Their arrangement within the downward sloping valley seems to suggest they are remnants of a large and ancient dam. 

“They would probably not have looked like modern concrete dams,” says Landreau. “They were more likely very broad embankments made of earth, marl, rubble and stone, possibly with stone protection on surfaces exposed to flowing water.”

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The strongest piece of evidence is a “zigzagging” feature at the centre of the structures, says Landreau, which would serve no purpose in a transport ramp or road, but, as a structure to relieve flood waters, makes perfect sense. Together, the features suggest they might be the earliest known duckbill weir-style dam ever built, which is a type of dam with an ability to manage floods. 

“By engineering a massive, two-stage dam system, they successfully tamed flash floods, stored millions of gallons of water and redirected it directly to the construction site,” says team member at Cairo University in Egypt. “This strongly suggests that the ancient Egyptians used water as a primary power source and transport mechanism to move multi-tonne blocks, fundamentally altering the historical narrative of how the pyramids were built.”

Snefru’s reign was associated other early hydrological projects, including the Sadd el-Kafara dam further north, which collapsed after a large flood. The new work suggests the putative dam near the Red Pyramid could have withstood powerful flooding from the Nile, indicating Snefru and his architects learned from their past mistakes.

“If confirmed through excavation, this research could significantly transform our understanding of 4th-dynasty construction logistics,” says at Egypt’s Ministry of Tourism and Antiquities.

DNA samples collected from Inca mummies have confirmed the presence of a strain of smallpox that first emerged in Europe.

“We interpreted this as the first direct molecular evidence of smallpox introduction into the Americas through European colonisation,” says at Trinity College Dublin, Ireland.

Smallpox was the scourge of humanity for centuries until its eradication in the 1980s, through vaccination, from all but a few high-security medical laboratories. Severe strains of the virus had a mortality rate of up to a third and left survivors with scars from the blisters and scabs that cover the skin and fill with pus.

The disease was particularly brutal in parts of the world colonised by Europeans, such as and the Americas, where Indigenous populations had no natural immunity, resulting in millions of deaths.

In the Americas, historical reports record that smallpox began devastating Indigenous communities in the early 16th century, after the arrival of European colonists.

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at the University of Dundee in the UK, who wasn’t involved in the new research, says the waves of epidemics, including smallpox, that spread across the Americas were some of the most important events in history. “These diseases killed perhaps 95 per cent of the Indigenous population of the Americas and allowed for European colonisation,” he says.

Nakagome and his colleagues studied samples of bone from mummies found at an archaeological site known as Camarones 9 in northern Chile, discovered in 1957. Over subsequent decades, 41 mummified bodies wrapped in blankets and buried with grave goods were recovered from the site.

“While the original aim was to study the human DNA, we also searched for DNA from ancient pathogens,” says Nakagome. “That is when we discovered fragments matching the smallpox virus in two individuals.”

The first was a woman who was 30 to 35 years old at the time of death, and the second, an 18-to-20-year-old man, was revealed by carbon dating to have died between 1492 and 1631.

By reconstructing the virus’s genomes and comparing them with other ancient and modern smallpox viruses, the team found that they belonged to a lineage of smallpox that includes early medieval and early modern European strains.

The discovery adds weight to the possibility that small skin lesions on the trunks of the mummies, previously attributed to chronic arsenic exposure, may in fact have been the distinctive pustules that scar the skin of smallpox victims.

“This finding allowed us to identify a small group of people impacted by the virus for which no historical record exists,” says team member at the University of Chile in Santiago. Before the new research, the pathogen was known only from historical accounts of large-scale outbreaks, she says.

The work was particularly sensitive because of the disturbance of the original remains and the loss of material during analysis, both considered extremely controversial subjects to Indigenous people and the scientific community. “We never forget that behind every DNA extraction is a person, not a data point,” says de la Fuente Castro.

Ward welcomed the new research. “Understanding exactly what was killing native peoples and why they were so susceptible to epidemic disease is a vitally important issue,” he says.

Historians are now trying to understand how Europeans deliberately or inadvertently fuelled the spread of epidemics like smallpox, he says. “Without these epidemics, colonisation of the Americas would have been very different.”