A chain

I noticed this today , on a tree beside the completely overgrown track which used to run up from the road to our house.    I am sure I have never seen it before, but it doesn't look as if it has been placed there recently.    I wonder if it was used to help haul a a mobile home  into a spot about twenty yards below it - but if so, why have I never noticed it (not that I walk the track very often I have  to admit given that in the summer the height of the bracken makes it almost impassable ) ?