Two teams of horses couldn't pull apart two empty metal bowls

In 1654, Otto von Guericke joined two copper hemispheres, pumped the air out with a vacuum pump of his own invention, and hitched horse teams to each side. With the air removed, atmospheric pressure alone held the sphere together so strongly that horses couldn't separate it — a public demonstration that convinced Europe vacuums were real and air had weight.

— Otto von Guericke, Experimenta Nova Magdeburgica de Vacuo Spatio — 1672