A now-dry branch of the Nile helped build Egypt’s pyramids, new study says

By Zoe Sottile, CNN

New evidence about the Nile bolsters a long-standing theory of how ancient Egyptians managed to build the massive pyramids of Giza thousands of years ago.

Researchers led by geographer Hader Sheisha at Aix-Marseille University in France used paleoecological clues to help reconstruct what Egypt’s Nile river might have looked like over the past 8,000 years.

They determined the pyramid builders likely took advantage of a “now-defunct” arm of the river to move construction materials, according a study published August 24 in the Proceedings of the National Academy of Sciences.

Their findings show “that the former waterscapes and higher river levels around 4,500 years ago facilitated the construction of the Giza Pyramid Complex,” the study said.

The Great Pyramid stands about 455 feet high and was commissioned by Pharaoh Khufu in the 26th century BC. Comprised of 2.3 million stone blocks with a combined mass of 5.75 million tons (that’s 16 times more than the Empire State Building), it’s the largest of the group of pyramids at Giza. The other two main pyramids belong to Khufu’s son Khafre and grandson Menkaure.

Built on the Giza plateau bordering Cairo, the structures — surrounded by temples, cemeteries and workers’ quarters — are the oldest of the Seven Wonders of the Ancient World.

Ancient engineers used floods like hydraulic lifts

Scientists have long theorized that ancient Egyptians must have exploited former parts of the Nile to move the tons of limestone and granite required to build the giant structures. (The Nile’s current waterways have moved too far away from the pyramid sites to be of use.)

This explanation, known as the “fluvial-port-complex” hypothesis, posits that ancient Egyptian engineers cut a small canal across from the site of the pyramid to the Nile’s Khufu branch, along the river’s western edge of the river’s flood plain, and dredged basins down to the river’s bottom. The annual flood waters functioned like a hydraulic lift, allowing them to move massive blocks of stone to the construction site, the researchers said.

But until now, scientists have lacked a specific understanding of which landscapes were involved, according to the researchers.

Using a combination of techniques to reconstruct the ancient Nile floodplain, the research team found that Egyptian engineers could have used the Nile’s now-dry Khufu branch to move construction materials to the site of the Giza pyramids.

First, they analyzed the rock layers of cores drilled in 2019 from the Giza floodplain to estimate water levels in the Khufu branch thousands of years ago. They also examined fossilized pollen grains from clay deposits in the Khufu area to identify vegetation-rich areas that are indicative of high water levels.

Their data showed that the Khufu area flourished during the first half of Egypt’s Old Kingdom period, from around 2700 to 2200 BC, when the building of the three main pyramids likely occurred.

The branch still had high water levels during the reigns of the pharaohs Khufu, Khafre and Menkaure.

“From the third to the fifth dynasties, the Khufu branch clearly offered an environment conducive to the emergence and development of the pyramid construction site, helping builders to plan the transport of stone and materials by boat,” the research team noted in the study.

But by Egypt’s Late Period, from around 525-332 BC, the Khufu branch’s water levels had fallen during a dry phase — a finding that is consistent with studies of the oxygen in mummies’ teeth and bones from the time period that reflect low water consumption, according to the study.

By the time Alexander the Great conquered Egypt in 332 BC, the Khufu branch was just a small channel.

Altogether, the data shows these ancient engineers used the Nile and its annual floods “to exploit the plateau area overlooking the floodplain for monumental construction.” In other words, the Nile’s bygone Khufu branch was indeed high enough to allow ancient engineers to move enormous blocks of stone — and construct the magnificent pyramids we know today.

Paleoclimatology affects our understanding of the past and future

For Joseph Manning, a classicist historian at Yale University, the “revolutionary” research is an example of how paleoclimatology is “fundamentally changing our understanding of human history.”

“We are getting a more realistic, and more dynamic understanding of human societies further back in time,” he told CNN.

These new techniques — like the pollen analysis used in this study — allow scientists to peer into societies thousands of years ago, Manning said.

“Climate science, like in this paper, is giving us fundamentally new information … (that is) very relevant to what’s happening today.” Understanding how climate changed during ancient Egypt’s Old Kingdom, for instance, gives scientists context for the climate change trends of today.

Previously, ancient Egypt historians depended primarily on texts to derive their understanding of Egyptian society, Manning said. But increasingly, environmental science is “throwing everything out the door” and allowing new insights about the ancient world.

The most novel part of the new research is that it identifies a naturally occurring waterway that could have been used to transport pyramid materials, whereas some researchers previously thought a man-made canal must have been needed, said Manning.

Making the most of environmental history will require scientists to collaborate and work with historians, he said. “There’s resistance to it, because it’s a different way of working,” Manning said.

But the possibilities, he added, are “super exciting.”

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