Roman Concrete May Offer Clues to How the Great Pyramid Was Built to Last

The Great Pyramid of Giza has endured for more than 4,500 years, but researchers still debate how ancient Egyptians assembled its estimated 2.3 million multiton blocks. A new study of Roman concrete may provide a materials-science clue for one controversial answer.

Mainstream archaeological thinking holds that the pyramid was built from natural limestone or granite blocks, cut precisely and hauled into place. An alternative theory proposes that at least some blocks were cast from an early form of concrete. Its central weakness has always been durability: how could artificial material survive thousands of years when some modern buildings deteriorate within decades?

Research published in the peer-reviewed journal Science Advances in July suggests that ancient Roman concrete could repair itself. A team led by Zhu Xiaohong of Beijing University of Technology examined concrete nearly 2,000 years old from a communal latrine at Hadrian’s Villa in Tivoli, Italy.

Using high-resolution imaging, the researchers found that the concrete’s durability came from calcite crystals that formed gradually inside its pores and microcracks. The crystals filled those weaknesses, helping the material resist decay and become stronger over centuries.

The study does not establish how the Great Pyramid was built, but it offers a possible answer to the durability problem facing the concrete hypothesis. The research team included scientists from the University of California, Berkeley, the University of Michigan, Lawrence Berkeley National Laboratory and the University of Illinois Urbana-Champaign.