Historians have long wondered how the ancient Egyptians could have built the pyramids out of stone blocks weighing several tons each, long before advanced construction equipment was invented. Researchers knew that the stones were hauled on sledges, but couldn't figure out how the workers kept those incredibly heavy sledges from sinking into the sand.
A new study has revealed the most likely answer: workers saturated the sand with water before moving the sledges, to form a solid, stable sliding surface. Says co-author Dr. Daniel Bonn, a professor of physics at the University of Amsterdam, "The water forms liquid bridges that glue the sand grains together, as in a sandcastle. The inspiration for the research was a tomb drawing that showed exactly this."
The scientists confirmed this finding by using a mini-sledge with a comparable amount of weight, to scale, over both dry and wet sand. When pulling it over the dry sand, hills of sand accumulated in front of the sledge, blocking the way; on wet sand, the path was smooth.