And the hoofs of the horses as they run shake the crumbling field....
- -- Publius Virgilius Maro, Roman poet (70-19 B.C.)
I have several video segments where I stood and filmed as the herd thundered toward me. It IS impressive, and you can FEEL the noise in your bones. They DO thunder. The ground DOES shake. And I don't have a whole army of them... but 20+ is ENOUGH. You get the effect.