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# Physicists Have A Simple Answer For How Egyptians Built The Pyramids

The Great Pyramid of Giza is the last of the ancient world's "seven wonders." The 4,500-year-old structure was constructed from 2.4 million limestone blocks, most weighing around 2.5 tons. Today we're still debating how the Egyptians managed to move these blocks from local quarries. Now scientists have a new hypothesis.

[Image: Library of Congress]

They rolled them.

Actually, to be more precise, this new idea is a variation of an older idea, which theorized that the Egyptians attached circle rockers to the blocks, turning them into cylinders that could easily be rolled to their destination. But, as the Physics arXiv blog points out, this ideas has some flaws: the cylinders would have exerted huge pressure on the ground causing considerable damage to roads. Modern estimates of the rate at which the pyramid was built suggest that workers moved some 40 blocks per day. If so, then even well-engineered roads would have required considerable maintenance.

In a recently published paper, Indiana University physicist Joseph West and some colleagues propose a different approach that considerably reduces the ground pressure but at the same time allows the blocks to be moved with significantly less effort than dragging them.

As Physics arXiv notes:

Their idea is remarkably simple. They strap wooden rods to a block, turning its profile from a square into a dodecagon, which can then be moved more easily by rolling.

West and co have tested their idea on a scale model consisting of a concrete block the shape of the square prism. This block was 20 cm square; 40 cm long and weighed almost 30 kilograms. They attached a set of three wooden dowel rods to each face of the block transforming its cross-section from a square to dodecagon.

Finally, they attached a rope to the top of the block and measured the force required to set the block rolling. Their measurements indicate that the block experiences a coefficient of dynamic friction equal to 0.3, for a steady rolling motion. This would require the crew to apply force of only 0.15 times the weight of the stone to pull a rope wrapped around the block.

They go on to calculate that a work crew of around 50 fit men would be required to move a block with a mass of 2.5 tons at the speed of 0.5 meters per second. "For full scale pyramid blocks, the wooden "rods" would need to be posts of order 30 cm in diameter, similar in size to those used as masts on ships in the Nile," say West and co.