It seems like they've almost written more than Tolkien at this point.

The Lord of the Rings Online team is at it again with another Lorebook update:

In the southern reaches of the Barrow-downs lies the Great Barrow, Othrongroth, one of the oldest and largest of the Edain mounds. As the Witch-king’s power has grown, fell spirits have taken possession of the rotting remains of the dead in his name. What was once a sacred place of solemnity is now the home to evil lurking in the shadows.

Read all about it at the LoTRO Lorebook.