The Pyramids of Giza and 27 others located around them were built on the banks of a branch of the Nile that is now disappeared, covered by desert sand and farmland. The discovery, resulting from a combination of satellite images, geophysical analysis, and sediment studies, shows the importance that the river had for ancient Egyptian societies, both as a cultural artery and for transporting construction materials.

In an article published last Thursday in the journal Communications Earth

The scientists who have led the discovery have named the extinct river branch, 64 kilometers long, as Ahmarat, which means pyramid in Egyptian. Located near the ruins of Memphis, once the capital of Ancient Egypt, the river connected the 31 temples spread between El Lisht and Giza. Its existence solves the mystery of why these structures are concentrated in a narrow strip amidst what is now an inhospitable desert.

The transportation of materials and labor to build the pyramids required a river that had remained hidden until now. Ahmarat has revealed that the river not only played a key role in the construction of the pyramids but also in receiving visitors. Each pyramid complex was directly connected to the river by raised causeways perpendicular to its course, which ended at a temple located at the water’s edge, serving as a port.

The position of each pyramid is not random either, but reflects the changes in climatic conditions over the 1,000 years during which the buildings were erected. When the first ones were built 4,700 years ago, the flow of the river’s branch was very high, so these pyramids are distant from the river and located on high ground to protect themselves from floods.

As the construction years progress, the pyramids are getting closer and closer to the river and to lower ground, reflecting the reduction of the flow, accelerated 4,200 years ago by a drought that limited the availability of water until almost drying up the branch. The latest constructions, 3,600 years old, are touching the shore of what used to be Ahmarat.

The discovery of the extinct river branch has been key thanks to the Synthetic Aperture Radar (SAR) onboard Sentinel-1, a satellite of the European Space Agency. This instrument emits radio waves that penetrate layers of fine sand, bounce off more compact natural and artificial structures located underneath, and return to the satellite. The result is a high-resolution image of the desert subsurface, offering a way to unearth secrets hidden beneath the sand.

This, the authors indicate, is an extremely useful tool to make excavations more efficient. Satellite images highlight points of archaeological and anthropological interest, which can then be further explored on-site. In fact, it is something that researchers have done in the Ahmarat layout.

Once the 64 kilometers of the river branch were located, they analyzed a section of just one kilometer using geophysical techniques to validate the satellite results. They also studied the sediments from two specific points to describe the composition of the ancient riverbed more accurately.

In addition to improving efficiency in research, experts suggest in the article using these satellite imaging techniques to protect ancient settlements yet to be discovered from the rapid urbanization of present-day Egypt. It is likely, they claim, that unknown towns and cities were built on the banks of Ahmarat, which finer analysis should be able to detect.