Bridges

The two rocks at the side are placed there at least 1500 years ago, maybe a thousand years earlier still, depending on what they are a part of. 

One interesting theory about these large, standing stones is that they were part of a symbol, not a grave at all. They were placed in a triangle but very often, as maybe in this case, one of the rocks has been removed because it has been in the way of farming earlier in history. Today there are laws against moving ancient remains like this. 

The theory says that the triangle was a symbol of the three roots from the Ash-tree "Yggdrasil", the world tree, of which our earth was a small part. Often in these formations you can find a pit right in the middle of the triangle where there could have been a tree or a stick, representing the tree. Archeologists seldom find any burials in these formations, more often burned bones from people or animals, which could mean they are cult-places, creating a bridge between people, holding the clan or the nearby population gathered. These rocks are placed at the highest point and we know that one of the mightiest chiefs on the island had a farm and a longhouse here. 

The modern bridge between the mainland and the island has the same purpose, we may not burn people or animals to keep it upright, instead we burn fossilised fuel in order to make it necessary for us.