When building the famous Pyramids of Gizeh around 4,600 years ago, the Egyptian master builders were helped by the climate. At that time, a side arm of the Nile reached directly to the plateau of Giza - and thus made it possible to transport the heavy stone blocks to the pyramid construction site, as researchers have found out. According to their reconstruction, this Khufu tributary still carried enough water to be navigable during the first half of the Old Kingdom. Only later did it increasingly dry out.
The three great pyramids of Giza are world famous and were already counted among the seven wonders of the world in ancient times. They originated from 2620 to 2500 BC during the fourth dynasty and were commissioned by the pharaohs Cheops, Chefre and Menkaure. They were built on a large limestone plateau that is now almost ten kilometers from the west bank of the Nile.
How did the stone blocks get to the pyramid construction site?
How the workers transported the stone blocks, which weighed several tons and had been brought from various quarries to the pyramid construction site on the Gizeh Plateau, has only been partially clarified so far. However, archaeologists have suspected for a long time that at the time of construction there was a side arm of the Nile which has now dried up and which led to the pyramid plateau. "The river port hypothesis posits that the pyramid builders dug a canal through the west bank of this branch of Cheops and deepened the branch," explain Hader Sheisha of the University of Aix-Marseille and his colleagues. As a result, according to the hypothesis, the stone blocks for building the pyramids could be brought right up to the plateau and unloaded there.
Possible relics of such port facilities and canals have already been found east of the Giza plateau. However, it has so far remained unclear whether the level of the Nile and its Cheops tributary was high enough at the time to enable this ship transport to the plateau. Sheisha and his team have now examined this in more detail using five drill cores from the area of the former arm of the Nile. Using rock and pollen analyzes and climate models, they were able to reconstruct the water level over 8000 years.
Cheops arm with navigable draft
The analyzes showed that the climate in Egypt and also on the upper reaches of the Nile was about 3500 BC. BC was relatively humid and the water levels of the Nile and Cheops arm were correspondingly high. However, the levels then dropped somewhat, allowing people in the predynastic period and early Egyptian empire to settle in the fertile lowlands of the riverbanks. "The attractiveness of Giza during the fourth millennium BC may be closely related to this drop in river levels," Sheisha and his team explain. From about 2970 BC The climate went through a period in which the annual floods of the Nile were only weak.
Nevertheless, the water level in the Cheops tributary was still high enough to be navigable, as the archaeologists determined. The pharaohs in particular benefited from this in the first half of the Old Kingdom from around 2686 BC. "From the third to fifth dynasties, the arm of Cheops was well suited to create and develop the pyramid site," the scholars explain. "The engineers of the Old Kingdom took advantage of the riverine environment and annual flooding of the Nile to build their monumental structures on the plateau," Sheisha and his colleagues say. The builders had parts of the Cheopsarm deepened and built canals and docks to better unload the cargo.
Especially during the annual Nile floods, even heavily loaded freighters could drive almost directly to the pyramid construction site. "As a result, the number of archaeological buildings on the plateau of Giza increased rapidly, especially during the fourth dynasty." The pharaohs Cheops, Chefre and Menkaure used this to set up a monument with the great pyramids that is unique to this day.
Navigability ended at the end of the Old Kingdom
Towards the end of the Old Kingdom from about 2225 BC. the water levels in the Cheops branch of the Nile began to fluctuate sharply. A little later there was even a dry period in North Africa, which prevented even the annual flooding of the Nile. "It is believed that this failure triggered severe famines that brought about the end of the Old Kingdom and the beginning of the First Intermediate Period," Sheisha and his team explain. In the centuries that followed, the climate and water levels fluctuated significantly again and again, until around the beginning of the reign of Pharaoh Tutankhamun in 1349, another dry period loomed. At the beginning of the Third Intermediate Period, the water levels of the Nile and the Cheops branch reached a new low, as a result of which the Cheops branch gradually silted up. Since then it has dried up.
Source: Proceedings of the National Academy of Sciences, doi: 10.1073/pnas.2202530119