In a new study, a Franco-American team found out that the ancient Egyptians built the great Pyramids by pouring concrete into blocks.

The theory that the giant stone blocks would have been made at high points on the site rather than being hauled upwards was first formulated by French chemist Joseph Davidovits but has been rejected by Egyptologists.

The theory sustains that parts of the pyramids were constructed using natural limestone while other parts were man-made by reconstituting liquefied lime.

The researchers used X-rays, plasma torch and electron microscopes to compare the composition of the stones. French Professor Gilles Hug, from the Office of National Aerospatial Studies and Research, and Egyptian-born Michel Barsoum, a professor at Philadelphia's Drexel University, analyzed the mineralogy of samples from the Giza pyramids. "Examination of the stone shows they could have been made from a kind of early concrete and poured into blocks." they said.

They might have discovered what would be the oldest known occurrence of concrete, explaining in part the mystery of how the Egyptians were able to erect such colossal structures. "The sophistication and endurance of this ancient concrete technology is simply astounding," they added.

But Egypt's antiquities minister Zahi Hawass strongly rejects the new studies.

"It was limestone, it's been studied before by hundreds of chemists," Hawass, who heads the Supreme Council of Antiquities.

"They're made from solid blocks of quarried limestone. We don't know the origin of these samples... We certainly never gave permission for anyone to take samples," he said.

Mark Lehner, a leading Egyptologist, also looks with caution at the new theory. "All studies of the stone have shown they are made mostly from limestone but also from basalt and granite mined in the region." "Where did these samples come from is the first important question," he told. "How did the French take samples for their tests without the Egyptians' permission?"