Ancient Egyptians used so much copper, they polluted the harbor near the pyramids, study finds

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 earlier, as laborers constructed the Great Pyramid, the contemporary dig spot lay on the sandy floor of Khufu Harbor.

In this ancient harbor—the world's oldest known port—researchers said they've identified the first major instance of human-induced metal contamination. Though the Giza necropolis is famous for its pyramids and shriveled mummies, a new study published in Geology offers unprecedented evidence of a largely unheralded aspect of ancient Egyptian civilization: persistent, centuries-long metalworking.

The discovery sheds light on life beyond the pharaonic and princely elites of ancient Egypt, researchers said. "We'd like to know more about 95% of the people rather than the elite," said Alain Véron, a geochemist from France's Aix-Marseille Université. His sentiments echo the thoughts of Christophe Morhange, a geoarchaeologist from the same institution, who underscored the importance of the sedimentary record in reconstructing historical narratives.

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"The sediments are as important as monuments," Morhange said, highlighting the often-overlooked significance of the ground beneath our feet.

A surprising history of contamination

The researchers used geochemical tracers to investigate metalworking activities around ancient Khufu Harbor. Located along a now defunct branch of the Nile near the Giza Plateau, the harbor was essential for transporting materials and was the site of a major copper toolmaking industry. These tools, some of which workers alloyed with arsenic for added durability, included blades, chisels, and drills to work materials like limestone, wood, and textiles. Researchers used inductively coupled plasma–mass spectrometry (ICP-MS) to measure levels of copper and arsenic, as well as of aluminum, iron, and titanium, with six carbon-14 dates to establish a chronological framework.

The study traced the onset of metal contamination to around 3265 BCE, earlier than researchers anticipated. Contamination during this Predynastic period suggests that human occupation and metalworking at Giza began more than 200 years earlier than previously documented.