The chemical secrets of a concrete Roman breakwater that has spent the last 2,000 years submerged in the Mediterranean Sea have been uncovered by an international team of researchers. The team has pinpointed why the best Roman concrete was superior to most modern concrete in durability, why its manufacture was less environmentally damaging, and how these improvements could be adopted in the modern world.

The team is led by Paulo Monteiro of the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), a professor of civil and environmental engineering at the University of California, Berkeley. Team member Marie Jackson did the analysis that revealed the key ingredient.

“It’s not that modern concrete isn’t good—it’s so good we use 19 billion tons of it a year,” says Monteiro. “The problem is that manufacturing Portland cement accounts for 7 percent of the carbon dioxide that industry puts into the air.”

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