The Egyptian pyramids are considered one of the Seven Wonders of the World, and it’s not surprising: when you stare at the massive structures, you can’t help but wonder, “How the hell did they do it?” The stones, some weighing 9,000 pounds, came from far away and needed to be dragged into place. Now, researchers from the University of Amsterdam believe they’ve discovered ancient Egyptians’ cunning strategy to move those massive stones: wet sand.