Physicists at the University of Amsterdam (UvA) have uncovered part of one of the great secrets of the ancient world: how did the ancient Egyptians build the pyramids?

According to the research, published in the prestigious Physical Review Letters, Egyptian builders used a clever trick.

Building the great pyramids

As the pyramids are made of stone blocks, building them required moving these very large and very heavy blocks across the desert. Archaeologists know that the blocks, quarried in places such as Anwar, were floated down the Nile on barges to be deposited near the building site at Giza.

Most Egyptologists also acknowledge that ramps were probably used to raise the blocks. According to a professor of Classics and ancient Mediterranean studies, if workers consistently raised the ramp course by course as the teams dragged their blocks up, the blocks could have been fitted into place fairly easily.

There was also evidence to suggest how they moved the blocks across the sand: the Twelfth Dynasty tomb of Djehutihotep has an illustration of 172 men pulling a sledge with an alabaster statue of him, estimated to weigh 60 tons.

Estimates based on this illustration state that 45 workers would be required to start moving a 16.300 kg block, or eight workers to move a 2.750 kg block. Other blocks in the pyramids, however, weigh over 15 tons, and there are even several 70 to 80 ton blocks. This means every block required enormous amounts of manpower.

New science, ancient technique

Except, as these physicists have discovered, not as much as people think. The illustration has man standing on the front of the sledge, pouring water on the sand. Why he was doing that was not known for certain, until experiments at UvA demonstrated that the correct amount of dampness in sand halves the pulling force required.

The scientist use a laboratory version of the Egyptian sledge in a tray of sand. Then they determined both the required pulling force and the stiffness of the sand as a function of the quantity of water in the sand.

With the correct amount of water, wet desert sand is about twice as stiff as dry sand, meaning a sledge glides far more easily over damp sand simply because the sand does not pile up in front of the sledge as it does in the case of dry sand.

Modern-day applications

Just because no one is building pyramids anymore does not mean that this works has purely historical value.

The physicists state that we still do not fully understand the behaviour of granular material like sand, even though they are very common and include asphalt, concrete and coal.

Currently, granular material accounts for about 10 per cent of worldwide energy consumption. This research could be useful in examine how to optimise its transport and processing. Or perhaps if someone chooses to build a pyramid by hand.

Sources: UvA, Wikipedia