In new research on the Great Pyramids of Giza, a scientist says he has found more to their construction than cut natural limestone. Some original parts of the massive structures appear to be made of concrete blocks. If true, historians say, this would be the earliest known application of concrete technology, some 2500 years before the Romans started using it widely in harbors, amphitheaters, and other architecture.

Reporting the results of his study, Michel W. Barsoum, a professor of materials engineering at Drexel University in Philadelphia, concluded that the use of limestone concrete could explain in part how the Egyptians were able to complete such massive monuments. They used concrete blocks, he said, on the outer and inner casings and probably on the upper levels where it would have been difficult to hoist carved stone. The full report appeared in the December 2006 issue of The Journal of the American Ceramic Society.