Why do dogs circle before bed?

Dogs are well known to circle there beds before they lay down but why?

Some think that it's due to 'making the bed' as in they prepare there bed before they lie in it as we all do. They may have intrinsic methods to push down grass for sleeping as in 'making a nest'.

It could be that they do this because they are creating a place that is 'mine' as in there telling other dogs 'This is me, this is my space and stay away'.

Me personally? I think the dogs are searching the area to check for anything they don't want in there beds. If you watch a dog do this they always look into the place they will lay down? Yes.

For me it's something we all do.. we make sure the place we go to sleep is safe.