• Fossilized pollen shows grasses and marshes once reached near the site of the Great Pyramid of Giza.
  • An aridification of East Africa likely depleted the branch of the Nile River that flowed close to the pyramid site.
  • The Great Pyramid of Giza stood as the tallest constructed structure for about 4,000 years.

Researchers believe a river running right up close to the Great Pyramid of Giza made getting the enormous stones to the site much easier, enabling construction of what was the world’s tallest human-made structure for about 4,000 years.

A group of researchers from France, China, and Egypt collaborated on a project to track fossilized pollen grains in the sediment around Giza to reconstruct the possibility of a waterway, a branch of the Nile, helping builders craft the Giza Pyramid Complex.

“Palaeoecological analyses have helped to reconstruct an 8,000-year fluvial history of the Nile in this area, showing that the former waterscapes and higher river levels around 4,500 years ago facilitated the construction of the Giza Pyramid Complex,” they write in a new paper published late last month in the journal Proceedings of the National Academy of Sciences. “The pyramids of Giza originally overlooked a new defunct arm of the Nile.”

More From Popular Mechanics
preview for Popular Mechanics All Sections

The team says the Khufu branch of the Nile River enabled navigation to the Pyramid Harbor complex, but the precise environmental history was unclear. So, to figure it out, the group relied on pollen-derived vegetation patterns to reconstruct fluvial variations on the Giza floodplain.

“After a high-stand level concomitant with the African Humid Period, our results show that Giza’s waterscapes responded to a gradual insolation-driven aridification of East Africa, with the lowest Nile levels recorded at the end of the Dynastic Period,” the authors write.

With the Nile just over four miles away from Giza now, it was probably much closer during the construction of the pyramids. The team concludes the Khufu branch 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 Great Pyramid of Giza originally rose 455 feet high with a mix of limestone, granite, and mortar.

The researchers pried into the fossilized pollen grains trapped in the area’s sediment and rock layers. The data showed flowering grasses were found near the site—the same grasses that still line the Nile, and additional evidence of marsh plants, the kind that take time to develop around the edges of bodies of water. This led the researchers to determine the water flow near Giza was a way of life until the area started to dry out in the era following the construction of the pyramids.

Additional studies of bones and teeth corroborate the timing of the Egyptian aridification.