At least a part of the mystery of how ancient Egyptians built the pyramids has been solved, Dutch researchers report, and it's all down to sand and a little water, they say.
It has long been a puzzle how the large stones needed to build the pyramids, some weighing as much as 9,000 pounds, could have been hauled long distances through the desert to the construction sites.
Wooden sleds with the stones lashed to them have long been considered the likely method, but the weight of the stones would have caused considerable friction between the sleds' runners and the sand beneath, making it hard for humans or even camels to make any appreciable progress in dragging the sleds across the desert.
With each motion forward of the sled, sand would pile up in front of its runners, impeding its progress, requiring continuous additional effort to clear it away.
The solution, University of Amsterdam researchers said in a published study, was a "clever trick" to defeat that friction using a little water on the sand over which the sleds traveled.
That created a more rigid surface, and kept the sleds' runners from digging into the sand while reducing the friction between runners and sand, they said.
"The water forms liquid bridges that glue the sand grains together, as in a sandcastle," study co-author and physicist Daniel Bonn said.
In addition to reducing the friction, the firmer sand would not tend to pile up ahead of the runners as the dry sand did.
Evidence for the technique has been discovered in a drawing in an ancient Egyptian tomb, which shows a weighted sled being pulled by a large number of men while a single man on the front of it is depicted pouring water in front of the runners.
Many Egyptologists had interpreted the pouring of water part of a ritual of purification but had ignored a possible scientific explanation, the Dutch researchers said.
To test their theory they pulled a small sled over a bed if dry sand and then again over sand that had been wetted with water.
"I was very surprised by the amount the pulling force could be reduced -- by as much as 50 percent -- meaning that the Egyptians needed only half the men to pull over wet sand as compared to dry," Bonn said.
