What is a lightning rod? How it protects the buildings?

Lightning rod is a device used to secure tall buildings from the effect of lightning. A metallic rod taller than the height of the building to be protected is installed in the walls of the building during its construction. One end of the rod is kept out in the air and the other is fixed in the ground. This provides easy route for transfer of electric discharge to the ground. Several such rods would be required to safeguard a building with a large area.