Ancient guy - "Hey aliens, can you share with us the secrets of flight, space travel or any other super advanced technology that got you here so that we might use that technology to better our lives and the lives of everyone else on this planet, or at the very least could you leave a piece of your technology with us, like a ship or something, so that we can study it and have proof that you came to visit us from outer space?
Alien - "No, but what if we put those huge rocks into a circle for you?"
Ancient guy - "OK"