Vanished arm of Nile helped ancient Egyptians transport pyramid materials

When the ancient Egyptians built the pyramids of Giza around 4,500 years ago, the Nile River had an arm — one that has long since vanished — with high water levels that helped laborers ship materials to their construction site, a new study finds.

The discovery builds on previous archaeological and historical findings that the Nile had an extra arm flowing by the pyramids. But now, by analyzing ancient pollen samples taken from earthen cores, it's clear that "the former waterscapes and higher river levels" gave the Giza Pyramid's builders a leg up, a team of researchers wrote in a paper published Aug. 29 in the journal the Proceedings of the National Academy of Sciences.

The research sheds light on how the pyramids — royal tombs for the pharaohs Khufu, Khafre and Menkaure — rose to monumental heights. Their towering stature was achieved, in large part, thanks to the Nile's now-defunct Khufu branch, which "remained at a high-water level during the reigns of Khufu, Khafre, and Menkaure, facilitating the transportation of construction materials to the Giza Pyramid Complex," the team wrote in their paper.

Related: What did ancient Egypt's pharaohs stash inside the pyramids?

Researchers have known for decades that the long-gone Khufu branch extended up to the Giza plateau in ancient times, but the new project aimed to find exactly how the water levels had changed over the past 8,000 years. 

To reconstruct the Nile's past, in May 2019 the team drilled five cores into the Giza floodplain. The researchers measured the amount of pollen found in different parts of the cores to determine how pollen levels had changed over time. Time periods when water was plentiful should have more pollen than periods that were arid, the study authors wrote. 

The pollen analysis revealed that at the time the ancient Egyptians built the Giza pyramids, water was plentiful enough that the Khufu branch would have flowed near the Giza pyramids. "It was a natural canal in the time of the fourth dynasty [when the pyramids were built]," study lead author Hader Sheisha, a physical geographer at Aix-Marseille University in France, told Live Science in an email. 

Sheisha noted that the water level was important for pyramid construction. "It would be very difficult if not impossible to build the pyramids without the Khufu branch and without it having a good level, which provides enough accommodation space for the boats carrying such heavy blocks of stone," she said. When exactly the branch went extinct is not certain, but the research shows that by 2,400 years ago the water level of the branch was very low.

The finds fit well with previous archaeological finds, which revealed a harbor close to the pyramids, as well as ancient papyri records that detailed workers bringing limestone to Giza via boat, the team noted in their paper. 

Live Science contacted several experts not involved with the research to get their thoughts. Most were unable to comment at press time, but one who did, Judith Bunbury, a geo-archaeologist at the University of Cambridge in the United Kingdom, praised the research. 

"The paper is an exciting contribution to our understanding of the dialogue between humans and their environment in Egypt within the context of changing climate," Bunbury told Live Science in an email.

Originally published on Live Science.