Study: Clues to Pyramids' Construction Were in the Sand

Today, nearly four miles of parched desert separate Egypt’s Giza pyramid complex from the Nile River, but that was not always case. In fact, the New York Times reports recent research suggests that a long-lost tributary of the Nile once flowed to the doorsteps of the Giza pyramids, and the findings may resolve a persistent mystery about how ancient engineers moved millions of two-ton limestone blocks to their present location. In a paper published last month in the Proceedings of the National Academy of Sciences, researchers assert that the so-called Khufu Branch—named for the Fourth Dynasty pharaoh entombed in the Great Pyramid—once stretched from the present-day banks of the Nile to Giza, and the evidence lies deep in the sand.

It's no surprise that Egyptian engineers relied on the Nile. Per Live Science, previously discovered papyrus scrolls detail how workers transported stones on the river, and there is archaeological evidence of a harbor near Giza complex. But until now, archaeologists could only hypothesize as to why and how that harbor existed. Researchers turned to the palaeoecological record. After determining the lost waterway’s probable location, they collected five sediment cores to a depth of 30 feet—enough to capture "a sedimentary time-lapse of Giza across thousands of years," as the Times puts it.

Using the ancient pollen grains contained in the cores, the team identified 61 different plant species concentrated in various layers, including cattails and papyrus indicating a marshy environment and flowering grasses like those found along the Nile’s banks today, per Phys.org. Comparing their results with previous geologic studies, the team "reconstructed" the Khufu’s ebb and flow since the end of the African Humid period, when North Africa was far wetter than today. Beginning about 8,000 years ago, the waters around Giza subsided, but the Khufu Branch remained as a viable waterway for millennia, until it was finally isolated due to gradual aridification of the region. By Tutankhamun’s time, the Khufu Branch had dropped substantially, and it was completely dry by about 600BC. (More Giza stories.)