You cannot see the wind but we all know it exists through the effects it has.
I think Von Daniked alluded to the fact that a possible explanation for structures that could not have been built by humans would have been built by aliens. After all - it was written in the Sumerian tablets.
The Sumerian Tablets tell the story of the creation of human beings. They tell how they created a race that is more developed than the Homo Erectus species by using the DNA of primates and their own DNA, and to use them as slave workers.
As you cannot understand the Sumerian tablets - you must believe they are not credible
