The levels of copper were “5 to 6 times higher than the natural background,” Alain Véron, a faculty member at France’s Aix-Marseille University who worked on the study, told Eos.

On a warm spring day in 2019, researchers bored into the earth beneath Cairo’s urban streets. Just over a kilometer away, the Great Pyramid of Giza shimmered on the horizon. Some 4,600 years ...