Ancient Egyptians used animal fats and vegetable oils to move massive stone blocks for pyramids, as evidenced by tomb paintings showing workers pouring liquid in front of sledges. Recent experiments proved that wetting sand with the right amount of water or oil reduces friction by half, allowing a team to pull twice the weight. Archaeologists found actual residues of tallow and oils on ancient sledge remains in burial sites. This 4,500-year-old lubrication technology was so effective that some historians believe it was the key engineering secret behind building the pyramids.