"It was one of the seven wonders of the ancient world, and the only one of them to remain standing today. Yet the story of how the Great Pyramid of Giza was actually built has remained a mystery for more than four millennia - until, perhaps, now.
A French architect believes he has finally solved one of the most puzzling construction problems in history by working out how the ancient Egyptians built such a massive structure without the benefit of iron tools, pulleys or wheels.
In Paris tomorrow, Jean-Pierre Houdin will unveil the fruits of eight years' work by describing at a conference how the pyramid of the pharaoh Khufu was built from the inside out. He will propose that the Egyptians carried the building blocks up an internal ramp that formed a spiral tunnel within the structure's outer wall. These tunnels, he believes, must still exist today.
With the help of sophisticated computer software developed by the French company Dassault Systemes, M. Houdin has been able to reconstruct a three-dimensional simulation of how the great limestone and granite blocks of the pyramid were put together stone by stone.
The simulation shows the logic behind building such a pyramid from the inside out. M. Houdin even believes he has solved the mystery of the king's chamber - why it had five granite ceilings instead of one, and how these great granite blocks were lifted to such a height.
The first recorded attempt to explain how the Pyramid of Khufu was built came from Herodotus, the Greek historian, who travelled to Egypt in about 450BC. Herodotus said that thousands of slaves dragged the stones to the site, which were then lifted up from one step of the pyramid to the next by a series of machines. The trouble with this, however, is that it was written about 2,000 years after the great pyramid was built.
Mechanical engineers today believe that it was unlikely that this was done with the limited technology of the time, especially when some of the granite stones of the king's chamber weigh up to 60 tons.
Another theory is that a giant external ramp was built to take the stones to the highest points on the pyramid. But such a ramp could not have had an incline any greater than 7 or 8 per cent, which would mean it must have been a mile long to build a structure 146 metres tall.
Such a ramp would also require as much building material as the pyramid itself - an unlikely scenario.
Others suggested that the ramp may have been wound around the outside of the pyramid as it grew. But such a ramp would have been prone to collapsing without being firmly fixed to the pyramid - and there is no evidence of any fixing points remaining on the outside of the pyramid today.
An external ramp would also raise the issue of where the waste products from the building went. What happened to such immense volumes of waste material when the pyramid was finished? There is no evidence of it today.
M. Houdin's explanation is that the "spoil" has been left within the pyramid because the internal, spiral ramp built a few metres inside the outer wall was left behind and remains there to this day.
"I am an architect - in my brain I have a 3-D computer," M. Houdin explained in an interview with The Independent. "My idea is that the pyramid was two different projects. The first was to build the volume of the pyramid and the second problem was to build the king's chamber."
According to his theory, the first stage of construction used a traditional external ramp that led up to a height of 43 metres from the base. Once completed, this volume of material would account for more than 70 per cent of the pyramid's total mass.
The next stage involved building the internal ramp in the shape of a spiral. "It was like a tunnel with a covered roof, but open to the sky at the four corners of the pyramid so that the stone blocks could be turned," M. Houdin said.
He has calculated that at a gentle incline of 7 per cent, such a ramp would be about a mile long as it wound itself up to a point just short of the pyramid's summit. One-ton blocks were hauled up this ramp by teams of eight to 10 men.
M. Houdin believes that the stone blocks used to construct the external ramp were eventually "recycled" by taking them up the internal ramp to the upper parts of the pyramid above the king's chamber.
Once the bulk of the pyramid was finished, the open corners of the ramp were filled in as the pyramid was finished off, but the ramp's tunnels were left empty.
The crucial piece of evidence in support of an internal network of spiral tunnels comes from a microgravity test carried out in 1986, he said. French scientists found a peculiar anomaly - a less-dense structure in the form of a spiral within the pyramid.
"They had it in the drawer for 15 years because it could not be explained. But when we put my drawings over it, there it was," M. Houdin said. "It is strong evidence, but not proof, that the tunnels still exist inside the pyramid and that they were not filled in," he said.
As for the task of lifting the 60-ton granite blocks as high as the ceilings of the king's chamber, M. Houdin believes this was done using a system of counterweights dragged down the internal ramps as the granite blocks, which were attached by ropes on the other side, were hauled up.
He also believes that the reason for the five false ceilings above the king's chamber was to act as a weight-saving device. They prevented too much weight being brought to bear on the supporting arch above the chamber's ceilings.
M. Houdin now has to convince sceptical Egyptologists, who have been offered rival theories in the past, that his construction theory is correct.
Neal Spencer, of the British Museum, said that from what little he knows of it, M. Houdin's idea seems plausible. "It's not as outlandish as some of the theories put forward," he added. "Elements of the idea might be reasonable, but the thing is to find the archaeological evidence to support it."
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