Getting to the point: how rolling stones helped build the pyramids

Theory of evolution: an engineer's view Egyptian men at work

How did they do that? As far as building the pyramids goes, the standard answer has for years been: by putting the 2.5-ton stones onto sledges and dragging them.

But now a Cambridge civil engineer has come up with a (literally) revolutionary explanation: that the individual stones were encased in two circular, hoop-like wooden runners, one at each end, and then rolled from the quarries and up ramps to the construction point.

The same "rolling-stones" method might helped transport those used to build Stonehenge, suggests Dr Dick Parry, formerly of Cambridge University's engineering department. To back up his pyramid hypothesis, Dr Parry has reconstructed full-scale models and shown that, with the rollers, three men can pull a stone which would otherwise need the efforts of 20.

The stones can also be rolled up ramps as steep as 1 in 4, whereas friction makes it impossible to pull a sledge up more than 1 in 10. Using sledges to build the pyramids, which are more than 130 metres high, would have required solid ramps a kilometre long - impossible given the site. With the rolling stones, ramps could be much shorter and more easily moved.

That would be important in building a structure of 2.3 million blocks weighing an average of 2.5 tons. "The logistics mean that over 20 years you would be quarrying and placing one stone every two minutes of the daylight hours," said Dr Parry, who gave a talk last night in Cambridge as part of National Science Week. "You need not ... brute force, but a hi-tech solution."

His suggestion also helps to answer the mystery of cradle-like objects discovered by archaeologists in the 1880s. These were thought to have been used to "rock" the stones upwards. Dr Parry laughs. "That doesn't explain how you get them from the quarry to the site," he said.

A number of reference books say that sledges were used to move large objects such as statues. But Dr Parry points out that those were one-off operations, where speed was immaterial; for the pyramids, it was essential.