It was built on a raised level area and surrounded by a ditch and a raised bank. It may have been built on top of an earlier structure. Research shows that the ditch used to be filled with water, and there was a large stone circle around the mound. The grave itself is a long narrow entrance opening into a large chamber. There are three smaller rooms which open into the main chamber. It has been built to line up with the sun at the Winter Solstice.