How an arm of the Nile that disappeared 2,500 years ago allowed the pyramids of Giza to be built

The construction of the imposing pyramids of Giza, some 4,500 years ago in the desert that extends on the west bank of the Nile, represents one of the greatest feats in the history of engineering and one that has aroused the most fascination and intrigue. especially when it comes to finding out how the ancient Egyptians raised them.

It is now accepted that the engineers of the time took advantage of an ancient branch of the Nile to transport the heavy materials used for its construction and all the supplies necessary to do so.

But today the river runs more than eight kilometers east of the pharaonic complex, and there is little evidence of the evolution of that landscape.

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In order to better understand this part of the puzzle, a group of scientists has now reconstructed 8,000 years of fluvial history of the Nile as it passes through the Giza Plateau from new sediment analyzes in the area, and has been able to show that the The water levels of that now-disappeared branch were ideal for erecting the pyramids.

“[These analyses] allow us to produce for the first time a good approximate record of the evolution of the vegetation [in the area] and to estimate the proximity or distance of the Nile from the pyramids.

It is very new," says Christophe Morhange, a geomorphologist at the University of Aix-Marseille and one of the authors of the study, published at the end of August in the American scientific journal

.

The study points out that today there is a broad consensus around the idea that to build the pyramids of Giza the engineers of the IV dynasty (2613-2494 years before the common era) relied on the help provided by an ancient branch of the Nile that they baptize as the branch of Cheops and that flowed along the western bank of the alluvial plain of the river.

Thanks to it, the ancient Egyptians were able to develop an ingenious system of canals, basins and a port - about which there are still many unanswered questions - at the foot of the Giza plateau, where today the three monumental pyramids rest.

Map reconstructing the Cheops branch of the Nile River. Proceedings of the National Academy of Sciences (PNAS)

The existence of the Cheops branch and all this water infrastructure built around it is supported by several archaeological finds made in the area and by evidence brought to light during modern urban projects carried out in Giza.

And part of the most transcendental information in this regard was provided by a set of papyri, discovered in 2013 in a port from the time of Pharaoh Cheops on the Red Sea coast, which testify to the presence of a port at the foot of the Giza plateau. and describing the transportation of material used to build the pyramids.

In order to better understand this landscape that facilitated the construction of the pyramids, the team led by Morhange extracted sediment from two boreholes about 15 meters deep in the Giza alluvial plain, where it is believed that the branch of Cheops, in search of new evidence of its existence.

The team then painstakingly analyzed the sediments for pollen grains buried over thousands of years that would allow them to piece together the plant history of the site.

In total, the study indicates that they found 61 species of plants, which they grouped into various vegetation patterns by proximity, and among which were common species on the banks of the Nile, others dragged by the river from tropical areas of its basin and some third indicative of a permanent body of water.

From here, the team has determined the changes in the water level of the place over millennia based on the greater or lesser abundance of the previous species in relation to other terrestrial ones.

“We use these patterns to define periods with wetter conditions around the Khufu Branch, indicating a higher level [of water] in the branch.

These humid conditions correspond with a greater representation of plant species such as those located on the banks of the Nile, Nilotic tropical taxa, and [species] that reveal the presence of a permanent body of water, ”says Hader Sheisha, environmental geographer at the University of Aix-Marseille and another of the authors of the study.

Illustration representing the pyramids of Giza and the port at the foot of the plateau. Alex Boersma

The results obtained have led the researchers to the conclusion that, although the Giza area had already begun a process of gradual aridification in the times of the pharaohs Cheops, Khafre and Mycerinus, when the three pyramids were built, the water level of Khufu's branch was tall enough to facilitate its construction.

The researchers' reconstruction shows that the highest levels of water in the Khufu branch were recorded during the African wet period—a time when North Africa and much of today's Sahara were very wet—and began to decline toward the west. 3550 before the common era.

This scenario, moreover, is consistent with the fact that during that same period there were human settlements along the eastern shore of the same Cheops branch, according to the study.

At the time the pyramids were built, on the other hand, the water levels of the branch of Cheops, always according to the study's estimates, were around 40% of their historical maximum, and when Tutankhamun ascended the throne in the year 1332 before the common era the branch had already been declining for centuries.

When Alexander the Great arrived in Egypt in 332 BCE, at the beginning of what would become known as the Ptolemaic period, the level of the Khufu branch was already "extremely low."

“The great contribution of the study is that it shows that sediments are essential if you want to understand [a process] between society and nature in the long term.

Nile sediments are crucial contextual indicators for archaeological excavations.

They are as important as the monuments themselves”, concludes Morhange.

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