When the Romans left and the Anglo Saxons took over they actually believed the stone structures of the Romans were in fact the work of a race of giants and refused to have anything to do with them. In that sort of circumstance it is easy to see how myths and legends can spring up from very little. All very chucklesome as are many of the early legends. Nowadays we tend to pour scorn upon the older myths and legends or have scientists and experts pour vast monies into the solving of them on the basis there is a kernel of truth in even the most lunatic of ideas. Then at the same time we create our own.
Crop circles have to be the classic example in the UK at the moment.
The huge weight of evidence suggests they are done by very human beings with very natural planks of wood but that is not good enough for some. Time and time again aliens have to be involved. There are some that accept it is humans having a bit of sport but then take it a bit further and suggest they are under alien influence, very Close Encounters. I suspect a good many are under very different influences. The Anglo Saxons didn't believe in beings from another planet, they believed in giants.