According to new research, they had a good reason for doing so – by wetting the sand, as little as half as much pulling force would have been required to move those sledges.

The research was conducted by a team from the Foundation for Fundamental Research on Matter, and the University of Amsterdam. They built miniature versions of the laden sledges, which they pulled through trays filled with both dry and moistened sand.

When an optimum amount of water was added to dry sand, capillary action bonded the individual grains together, causing the material to become approximately twice as stiff as it had been.