4,500 years ago, the pyramids of Giza hover over the west bank of the River Nile like a range of geometric mountains. The Great Pyramid, built to commemorate the reign of Pharaoh Khufu, the second king of Egypt’s fourth dynasty, occupies over 52,000 square meters and was over 140 meters high upon its completion, around 2560 BC.
Remarkably, ancient architects somehow transported 2.3 million blocks of limestone and granite, each weighing on average over 2 tons, across miles of desert from the banks of the Nile to the pyramid site on the Giza Plateau.
Transporting these stones overland would have been strenuous. Scientists have long believed that using a river or canal made the process possible, but today the Nile is miles away from the pyramids. On Monday, however, a team of researchers reported evidence that a lost tributary of the Nile once crossed this stretch of desert and would have greatly simplified the transport of the gigantic stones to the pyramid complex.
Using clues preserved in the desert floor, scientists reconstructed the rise and fall of the Khufu branch, a now-extinct tributary of the Nile, over the past 8,000 years. Their findings, published in the Proceedings of the National Academy of Science, propose that the Khufu branch, which dried up completely around 600 BC, played a critical role in building the ancient wonders.
“It would be impossible to build the pyramids here without this branch of the Nile,” said Hader Sheisha, an environmental geographer at the European Center for Research and Teaching in Environmental Geoscience and author of the new study.
The project was spurred by the discovery of a treasure trove of papyrus fragments at the site of an ancient harbor near the Red Sea in 2013. Some of the scrolls date back to the reign of Khufu and recount the efforts of an officer named Merer and his men to transport limestone uphill. the Nile to Giza, where it was shaped as the outer layer of the Great Pyramid.
“When I read about it,” said Sheisha, “I was very interested, because it confirms that the transport of materials for the construction of the pyramid was over water.”
Transporting goods on the Nile was nothing new, said Joseph Manning, a Yale University classicist who studied the effect of volcanic eruptions on the river during subsequent periods of Egyptian history and was not involved in the new research. “We know there was water near the pyramids at Giza; that’s how the stone was transported,” he said.
According to Manning, researchers theorized that ancient engineers could have carved canals in the desert or used a branch of the Nile to transport the pyramid’s materials, but evidence of these lost waterways was scant. This obscured the route Merer and others took to reach the port of Giza, the pyramid-building center located more than 6 kilometers west of the banks of the Nile.
Seeking evidence of an ancient river route, the researchers drilled into the desert near the port of Giza and along the hypothetical Khufu Branch route, where they collected five sediment cores. Digging more than 30 feet, they captured a sedimentary time-lapse of Giza that spans thousands of years.
In a laboratory in France, Sheisha and her colleagues scoured the nuclei for pollen grains, tiny but enduring environmental clues that help researchers identify plant life from the past.
They found 61 plant species, including ferns, palms and sedges that were concentrated in different parts of the core, providing insight into how the local ecosystem has changed over millennia, said Christophe Morhange, a geomorphologist at Aix-Marseille University in France, and one of the authors of the new study.
Pollen from plants such as cattail and papyrus indicated an aquatic, swampy environment, while pollen from drought-resistant plants such as grasses helped identify “when the Nile was furthest from the pyramids” in times of drought, Morhange said.
The researchers used data collected from pollen grains to estimate previous river levels and recreate Giza’s wet past. About 8,000 years ago, during a wet era known as the African Wet Period, during which much of the Sahara was covered in lakes and grasslands, the region around Giza was submerged.
Over the next thousands of years, as North Africa dried up, the Khufu Branch retained about 40% of its water. This made it a perfect element for building the pyramids, Sheisha said: the waterway remained deep enough to navigate easily, but not so high as to pose a great risk of flooding.
This shortcut to the pyramids was short-lived. As Egypt became even drier, the water level in the Khufu Branch dropped beyond usability, and construction of the pyramid ended. When King Tutankhamun assumed the throne around 1350 BC, the river had experienced centuries of gradual decline. When Alexander the Great conquered Egypt in 332 BC, the area around the parched Khufu Branch had been converted into a cemetery.
Although the water has long since disappeared, Sheisha believes that identifying how Giza’s natural environment favored the builders of the pyramids could help to shed light on some of the many mysteries that still surround the construction of the ancient geometric monuments. “Knowing more about the environment may solve part of the puzzle of building the pyramids,” she said.
Translated by Luiz Roberto M. Gonçalves
