External ramps figure in many previous theories of pyramid-building. One favors the use of a straight frontal ramp extending from the base to the summit; alternative approaches involve external ramps that zigzag up the triangular faces of a pyramid or spiral around the sides like a corkscrew. But all these theories have drawbacks, according to Bob Brier, an archaeologist at Long Island University who described Houdin's theory in the May/June issue of Archaeology.
A straight frontal ramp would require too much stone and labor if built to the full height of a pyramid, he explains. To maintain a manageable grade of 6 to 8 percent for the incline—the maximum slope of modern highways—such a ramp would have to extend a mile or more. Ramps surrounding a pyramid might block sight lines the builders needed to ensure their measurements were accurate, or be prone to collapsing.
Brier thinks Houdin has made a compelling case in his engineering analysis. "It's a radical idea, because of the ramp being internal, but it's possible, and it's worthy of being tested," Brier says. "It's not a perfect theory, but I think it's the most interesting archaeological theory we've had in a very long time."
Brier says he remains skeptical about whether internal passageways would have allowed the pyramid builders enough room to maneuver heavy stone blocks.
Craig B. Smith, an engineer who wrote How the Great Pyramid Was Built, also has some doubts about the new theory. "It adds an unnecessary degree of complexity, and I think of the ancient Egyptians as practical builders who reduced things to simple, practical approaches," says Smith. "Also, there is no evidence that internal ramps were used in any pyramid built before the Great Pyramid, or after."
Houdin is confident that internal passageways remain inside the Great Pyramid, obscured by outer layers of stones. He plans to test for their presence using non-invasive technologies such as infrared photography, radar, sonar and microgravimetry, which can detect hidden spaces in solid structures by measuring differences in density.
In partnership with archaeologists from around the world, Houdin applied for permission to do an on-site survey. He expects to get the go-ahead from Egyptian authorities in the next year or two.
Houdin has presented his theory to Zahi Hawass, secretary general of Egypt's Supreme Council on Antiquities. In the foreword to a recent book by Houdin, Khufu: The Secrets Behind the Building of the Great Pyramid, Zawass calls the work "an interesting, potentially promising, new line of investigation."
Diana Parsell is a writer and editor in Falls Church, Virginia.