I think the invention of verbal language is the greatest invention. It paved the way to transfer knowledge, communicate our thoughts and convey ideas. If it weren't for verbal language we would never have achieved all the greatness that we now brag about.

You can think all you want, formulate complex theories in your mind, imagine the unimaginable things and ponder upon the observations of the world around you but you can't achieve anything solid and practical unless you have a sophisticated way to communicate your ideas, theories and imaginations to people who can then help you build your dreams with their own skills and creativity.